Tag Archives: jQuery

LinkedIn jQuery Assessment

Here we have given the collection of jQuery Questions and Answers asked in Linked in assessment. LinkedIn Assessment is a test of particular skill. After passing this skill you will get a Bade in your profile and that you can share with your network.

Q1. What’s the difference between these two snippets?

$('button').on('click', function(){ alert('you clicked the button!'); });
$('button').click(function(){ alert('you clicked the button!'); });
  • Only the second one will work; jQuery does not have a function called .on.
  • The second snippet will not function.
  • Nothing .click(function) is shorter way to write .on('click', function).
  • The first snippet will execute for every button on the page, the second will only apply to the first button.

Q2. What does the following line of code do?

jQuery('p')

  • Loads a paragraph tag from a remote server using AJAX
  • Aliases jQuery to a variable p
  • Selects all paragraphs on the page
  • Creates a new paragraph tag and inserts it into the body tag

Q3. Given the following HTML, how could we use one line to hide or show the button?

<button class="btn btn-primary" type="submit">Continue to checkout</button>
  • $('.btn-primary').toggle();
  • $('.btn-primary').showHide();
  • $('.btn-primary').not(':visible').show();
  • $('.btn-primary').css({ display: 'block'});

Q4. Working with AJAX, we may run into situations where a piece of code should not be run until after multiple AJAX calls have completed successfully. Say we need to call two external services for JSON data (a list of students, and a list of classes). And only after retrieving those data will we perform some manipulations on a page. What is the preferred way for dealing with this scenario?

https://example.com/json-api/students
https://example.com/json-api/classes

  • [ ]
$.get([ 'https://example.com/json-api/students', 'https://example.com/json-api/classes' ], function(studentRequest, classRequest) { 
  // the rest of the code goes here 
});
  • [ ]
$.when( $.get('https://example.com/json-api/students'), $.get('https://example.com/json-api/classes') ).done(function(studentRequest, classRequest) { 
  // the rest of the code goes here 
});
  • [ ]
$.bind( $.get('https://example.com/json-api/students'), $.get('https://example.com/json-api/classes') ).done(function(studentRequest, classRequest) { 
  // the rest of the code goes here 
});
  • [x]
$.ajax('https://example.com/json-api/students', { success: function(studentRequest) { $.ajax('https://example.com/json-api/classes', { success: function(classRequest) { 
  // the rest of the code goes here 
} }); } });

Q5. Given the snippet of HTML below, what is the difference between the two lines that follow it?

<ul>
    <li>Item 1</li>
    <li>Item 2</li>
    <li>Item 3</li>
    <li>Item 4</li>
</ul>
$('ul').find('li').get(2);
$('ul').find('li').eq(2);
  • .get() retrieves a DOM element, and can’t be chained, eq() retrieves a jQuery object, and can be chained.
  • .get() retrieves a jQuery object, and can’t be chained, eq() retrieves a DOM element, and can be chained.
  • .get() retrieves a jQuery object, and is zero-indexed, eq() retrieves a DOM element, and is 1-indexed.
  • .get() retrieves a DOM element, and is zero-indexed, eq() retrieves a jQuery object, and is 1-indexed.

Q6. Suppose we want to have a ball created from an HTML element (id=ball) move down and to the right from its original location when clicked, and move back into its original place when finished. Given a starting point of this, which of these snippets would accomplish that goal?

$('#ball').click(function() {
  // Our code goes here
});
  • [x]
$(this).animate({ top: '+=100', left: '+=100', }, { duration: 600, complete: function() { $(this).animate({ top: '-=100', left: '-=100', }, 600) } });
  • [ ]
$(this).animate({ top: '-=100', left: '-=100', }, 600, function() { $(this).animate({ top: '+=100', left: '+=100', }, 600) });
  • [ ]
$(this).animate({ top: '=100', left: '=100', }, { duration: 600, complete: function() { $(this).animate({ top: 0, left: 0, }, 600) } });
  • [ ]
$(this).animate({ top: '100', left: '100', }, 600, function() { $(this).animate({ top: 0, left: 0, }, 600) });

Q7. Given the following CSS and HTML codes below, how could you apply the success class to the feedback div?

.success {
  color: green;
  background: #ddffdd;
}
<div class="feedback">
  Thank you for answering this survey.
</div>
  • $('.feedback').hasClass('.success');
  • $.css('.feedback', '.success');
  • $('.feedback').addClass('success');
  • $('.feedback').css('.success');

Q8. Below is an example page snippet that includes a couple of messages in a list, and a code snippet that retrieves a few hundred messages from a API endpoints using AJAX. How might we add these items to the page snippet in a way that avoids performance problems with DOM insertions?

<div class="message-area">
  <ul class="message-area--list">
    <li>Existing message 1</li>
    <li>Existing message 2</li>
  </ul>
</div>
$.get('//example.com/api/v1/message')
.done(function(data) {
  var tonsOfItems = data.messages;
  // add all these messages to a large page
});
  • tonsOfItems.map(function(item) { $('.message-area--list').append('<li>'+item+'</li>'); });
  • var tonsOfListItems = tonsOfItems.map(function(item)) { return '<li>'+item+'</li>'; }); $('.message-area--list').append(tonsOfListItems.join(''));
  • Removing the event handlers with JavaScript will be slower than removing them $.each(tonsOfItems, function(idx, item) { $('<li>'+item+'</li>').appendTo($messageList); });
  • $.each(tonsOfItems, function(idx, item) { $('.message-area--list').append('<li>'+item+'</li>'); });

Q9. What is jQuery?

  • jQuery is a bridge between Java and Javascript that makes native apps easier to write.
  • jQuery is a plugin for JavaScript that makes database queries easier to write.
  • jQuery is a collection of JavaScript functions that makes finding and manipulating elements on a page, AJAX, and other things easier.
  • jQuery is a Chrome extension that allows users to create their own extensions with just a few lines of JavaScript.

Q10. We want to create a new jQuery plugin called linkUpdater that can be chained onto other jQuery selector like a normal plugin. It should update all the links in the referenced collection so they open in new windows or tabs. Below is the first cut. What is one problem with this plugin?

"user strict";
($.linkUpdater = function() {
  this.find('a').attr('target', '_blank');
})( jQuery );
  • this needs to be wrapped, like $(this), in order to be chained in a plugin.
  • jQuery plugins can’t be safely authored in strict mode.
  • In order to be used by other code, plugins need to be added to the global namespace, not wrapped in a function expression.
  • Our plugin should extend jQuery.fn, not jQuery itself.

Q11. Generally speaking, when used on a web page, how should jQuery be installed, and why?

  • Just before the closing body tag, because we want to avoid blocking other resources from loading, and we use the ready method to make sure our code fires after the DOM is ready
  • Using the highest version number possible because only jQuery 3 and up are compatible with Internet Explorer 7
  • In the head tag because we want jQuery available as soon as possible
  • From a CDN because we want to be able to use jQuery online or offline

Q12. Given the following HTML, how could we make this button disappear from the page using jQuery?

<button class="btn btn-primary" type="submit">Continue to checkout</button>
  • $('.btn-primary').hide();
  • $('.btn-primary:visible').not();
  • $('.btn-primary').visibility(false);
  • $('.btn-primary').show(false);

Q13. What is the difference between $('header').html() and $('header').text()?

  • $('header').html() returns the inner HTML of the header. $('header').text() returns only the text
  • $('header').html() returns only the HTML tags used, without the text. $('header').text() returns only the text
  • $('header').html() strips all HTML from the header. $('header').text() always returns an empty string.
  • $('header').html() returns all headers in an HTML document. $('header').text() the first line of a text file.

Q14. When writing jQuery plugins, we often provide default options that may be overridden by the end user. What jQuery function is most useful for this purpose?

  • $.extend
  • $.clone
  • $.fn.extend
  • $.merge

Q15. There are times when you might want to programmatically trigger an event, instead of simply reacting to user input directly. Given this markup, Which choice will NOT cause a click event to the select box when the button is clicked?

<article>
  <div>
    Here's a button you can click: <button class="btn">Click Me</button>
  </div>
  <form>
    <p>
      Further down the page, there's a select box.
    </p>
    <select>
      <option value="1">One</option>
      <option value="2">One</option>
      <option value="3">One</option>
      <option value="4">One</option>
    </select>
  </form>
</article>
  • $('button').on('click.myApp', (function() { $('input[type=select]').trigger('click'); });
  • $('button').on('click', (function() { $('input[type=select]').click()); });
  • $('button').trigger(function() { $('input[type=select]').click(); });
  • $('button').click(function() { $('input[type=select]').click(); });

Q16. You have an absolutely positioned element inside a relatively positioned parent element, and you want to animate that element within its parent element. What jQuery function is most useful for finding the initial coordinates of the .animate-me?

<style>
  .parent {
    position: relative;
    top: 3em;
    width: 50%;
    min-height: 50vh;
    margin: 0 auto;
  }

  .animate-me {
    position: absolute;
    top: 40px;
    right: 30px;
  }
</style>

<div class="parent">
  <div class="animate-me">
    This box will move!
  </div>
</div>
  • $('.animate-me').offset();
  • $('.animate-me').each();
  • $('.animate-me').position();
  • $('.animate-me').offsetParent();

Q17. You want to work with AJAX using a Promise-like interface instead of nested callback functions. What jQuery API should you use?

  • jQuery.sub
  • jQuery.ajaxTransport
  • jQuery.Deferred
  • jQuery.proxy

Q18. What is tricky about jQuery’s nth- filters (:nth-child, :nth-of-type, etc.) relative to other filters?

  • Referring to lists of items, they are 1-indexed (like CSS), not 0-indexed (like JavaScript).
  • They don’t return the jQuery object, and cannot be chained.
  • They can return the wrong items if the DOM was recently manipulated.
  • They are not part of CSS, so they don’t get the performance benefits of passing through the document.querySelectorAll.

Q19. jQuery’s AJAX functions return objects that implement the Promise API. As a result, you can chain promises and avoid nested callbacks. What does that look like?

  • [x]
$.get('hhttp://httpbin.org/delay/2')
  .then(function(response) {
    // Data from first GET is here as 'response'
    return $.get('http://httpbin.org/delay/2');
  })
  .then(function(response) {
    // Data from second GET is here as 'response'
  });
  • [ ]
$.get('hhttp://httpbin.org/delay/2')
  .catch(function(response) {
    // Data from first GET is here as 'response'
    return $.get('http://httpbin.org/delay/2');
  })
  .done(function(response) {
    // Data from second GET is here as 'response'
  });
  • [ ]
$.get('hhttp://httpbin.org/delay/2', function(response1) {
  // Data from first GET is here as 'response1'

  $.get('http://httpbin.org/delay/2', function(response2) {
  // Data from second GET is here as 'response2'
  });
});
  • [ ]
$.get('hhttp://httpbin.org/delay/2')
  .then(function(response) {
    // Data from first GET is here as 'response'
    return response;
  })
  .get('http://httpbin.org/delay/2', function(response) {
    // Data from second GET is here as 'response'
  });

Q20. You want to have a ball that is created from an HTML element (id=ball) move down and to the right of its original location when clicked, and move back to its original place when finished. What snippet, added to the code below, would do this?

$('#ball').click(function() {
  // Our code goes here
});
  • [ ]
$(this).animate({
  top: '-=100',
  left: '-=100',
}, 600, function() {
  $(this).animate({
  top: '+=100',
  left: '+=100',
  }, 600)
});
  • [x]
$(this).animate({
  top: '+=100',
  left: '+=100',
}, {
  duration: 600,
  complete: function() {
  $(this).animate({
  top: '-=100',
  left: '-=100',
  }, 600)
  }
});
  • [ ]
$(this).animate({
  top: 100,
  left: 100,
}, 600, function() {
  $(this).animate({
  top: 0,
  left: 0,
  }, 600)
});
  • [ ]
$(this).animate({
  top: 100,
  left: 100,
}, {
  duration: 600,
  complete: function() {
  $(this).animate({
  top: 0,
  left: 0,
  }, 600)
  }
});

Q21. The way .wrap() works is sometimes misunderstood. Given the DOM and jQuery snippets below, what does the modified DOM snippet look like?

<div id="container">
  <div class="item">Here's an item</div>
</div>
$('#container').wrap('<div class="wrapper"></div>').css('border', '2px solid red');
  • [ ]
<div class="wrapper" style="border: 2px solid red;">
  <div id="container">
    <div class="item">Here's an item</div>
  </div>
</div>
  • [x]
<div class="wrapper">
  <div id="container" style="border: 2px solid red;">
    <div class="item">Here's an item</div>
  </div>
</div>
  • [ ]
<div id="container" style="border: 2px solid red;">
  <div class="wrapper">
    <div class="item">Here's an item</div>
  </div>
  </div>
  • [ ]
<div id="container">
  <div class="wrapper" style="border: 2px solid red;">
    <div class="item">Here's an item</div>
  </div>
</div>

Q22. How can you select the following blockquote AND the list in a single call to jQuery() without chaining?

<div class="quotes">
  <blockquote data-favorite="false">A quote</blockquote>
  <blockquote data-favorite="true">A favorite quote</blockquote>
  <blockquote data-favorite="false">A quote</blockquote>
  <blockquote data-favorite="false">A quote</blockquote>
</div>

<ul class="menu-first">
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
  <li>Item 4</li>
</ul>
  • $('.quotes + .menu-first')
  • $('.quotes .menu-first')
  • $('.quotes, .menu-first')
  • $('.quotes' + '.menu-first')

Q23. Effects like show, hide, fadIn, and fadeOut can be called with no arguments, but can also take arguments for how long they should last. Which is NOT a duration argument supported by these functions?

  • “fast”
  • “extreme”
  • 2000
  • “slow”

Q24. Though jQuery offers visual effects, it is considered a best practice to use CSS to set up different states triggered by classes, where it makes sense. What’s the easiest way to enable and disable a class bounce on an element with the ID dialog?

  • $('#dialog').classToggle('bounce')
  • $('#dialog.bounce').removeClass().addClass()
  • $('#dialog').addOrRemoveClass('bounce')
  • $('#dialog').toggleClass('bounce')

Q25. What is the main difference between selectors and filters?

  • Selectors are used to refine the content that filters have been applied to.
  • Selectors are used to find and select content in a page. Filters are used to refine the results of selectors.
  • Filters are used to remove content from the page. Selectors are used to add content to the page
  • There is no real difference. They are both used to build up lists of page content.

Q26. You want to create a custom right-click menu. How might you start the code?

  • $('#canvas').on('click.right', function(){ console.log('Handled a right-click') });
  • $('#canvas').on('contextual', function(){ console.log('Handled a right-click') });
  • $('#canvas').on('contextmenu', function(){ console.log('Handled a right-click') });
  • $('#canvas').on('rightclick', function(){ console.log('Handled a right-click') });

Q27. What is the correct way to check how many paragraphs exist on a page using jQuery?

  • $('p').count()
  • $('p').length
  • $('*').find('p')
  • $('p').length()

Q28. As with many areas of JavaScript, keeping track of the meaning of this is important and sometimes tricky. What does this mean at each of the two points in this custom plugin snippet?

$.fn.customPlugin = function() {
  // Point 1

  return this.each(function() {
    // Point 2
  })
}
$(document).customPlugin();
  • At Point 1, this means a jQuery object. At Point 2, it means a DOM element.
  • In this case, they mean the same thing: a jQuery object.
  • In this case, they mean the same thing: a DOM element.
  • At Point 1, this means a DOM element. At Point 2, it means a jQuery object.

Q29. How can you make the first list item bold and the next item oblique, in a single statement chain?

<ul class="menu-first">
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
  <li>Item 4</li>
</ul>
  • [ ]
$('.menu-first > li')
  .eq(0)
  .css('font-weight', 'bold')
  .eq(1)
  .css('font-style', 'oblique');
  • [ ]
$('.menu-first > li')
  .first()
  .css('font-weight', 'bold')
  .after()
  .css('font-style', 'oblique');
  • [ ]
$('.menu-first > li')
  .first()
  .css('font-weight', 'bold')
  .second()
  .css('font-style', 'oblique');
  • [x]
$('.menu-first > li')
  .eq(0)
  .css('font-weight', 'bold')
  .next()
  .css('font-style', 'oblique');

Q30. Which CSS selectors can you NOT use in jQuery?

  • You cannot use multiple class selectors such as .class1.class2.
  • You cannot use pseudo-classes such as :not or :last-of-type.
  • You cannot use IDs and classes together, such as #element.class.
  • None. All CSS selectors are compatible in jQuery.

Q31. Starting with some DOM elements in the nested structure below, you assign listeners for the same event to a child element and one of the parents using the JavaScript that follows. You want to ensure that when .leaf is clicked, only its event handler will be fired, instead of the click bubbling up and also firing the parent’s click handler. What do you need to add to its handler function?

<ul class="items" id="main-menu">
  <li>Item 1<ul>
    <li class="leaf">Sub Item 1</li>
    <li>Sub Item 2</li>
  </ul></li>
</ul>
$('.leaf').click( function(event) { console.log('Sub Item 1 got a click'); } );
$('#main-menu').click( function(event) { console.log('Main menu got a click'); } );
  • event.capture();
  • event.stopPropagation();
  • event.preventDefault();
  • event.stop();

Q32. Using event delegation, you can listen for events on a lot of different items without having to attach separate listeners to each one. But there are times when you may want to check the type of item receiving the event before doing anything, such as checking if an image was clicked versus a text field. Given the starter code below, which choice shows what jQuery provides to help with that process?

<div id="sidebar">
  <img src="fancy-button.png" alt="Pick Me">
  <input type="text" placeholder="Fill in something">
</div>
$('#sidebar').click(function(evt) {
  var $target = $(evt.target);

  // What goes here?
});
  • $($target.get(0) + ':image')
  • $('img').is($target)
  • $target.filter('img')
  • $target.is('img')

Q33. There are many ways to create elements that can be added to the page. Which answer is NOT one of those ways, assuming you have the following on the page?

<div id="elements"></div>
  • [ ]
$("#elements").append($('<p class="appended">As an HTML string</p>'));
  • [ ]
var p = document.createElement('p');
var text = document.createTextNode('As a DOM element');
p.appendChild(text);
$("#elements").append(p);
  • [x]
$("#elements").append(<p class="appended">As a JSX object</p>);
  • [ ]
$("#elements").append($('<p>', {
  "class": 'appended',
  'text': "As an attribute object"
}));

Q34. The .addClass() and .removeClass() methods can accept functions as arguments. What does this function do?

$('#menu').addClass(function() {
  return $('body').attr('class');
});
  • It adds the first class found on the body element to the #menu element.
  • It adds all classes found on the #menu element to the body tag.
  • It replaces any classes on the #menu element with all classes from the body tag.
  • It adds all classes found on the body element to the #menu element.

Q35. You’re working on a site that uses an old version of jQuery, and you want to update to a newer version. What’s the most efficient way to do so?

  • Install the newer version of jQuery, go through each script one by one, and fix what looks broken.
  • Read the change notes for the newer version of jQuery, fix all scripts, install the newer version, and fix anything that remains broken.
  • Install the newer version of jQuery as well as its Migrate plugin, fix all warnings, and uninstall the Migrate plugin.
  • Install the newer version of jQuery at the same time, and use jQuery.noConflict() on pages that need the older version.

Q36. Let’s say you have a page with just one link on it. How can you change the anchor tag so it links to example.com?

  • $('a').attribute('href', 'http://www.example.com')
  • $('a').attr('href', 'http://www.example.com')
  • $('a').data('href', 'http://www.example.com')
  • $('a').href('http://www.example.com')

Q37. What does $() mean in jQuery?

  • It is an alias to the main core method of jQuery itself—the same as writing jQuery().
  • It is a utility function that selects the first element from the document.
  • It is a shorter way to write document.getElementById().
  • It is a utility function that selects the last element from the document.

Q38. Along with DOM traversal and manipulation, jQuery offers several general-purpose helper functions that fill in some JavaScript gaps, especially before ES2015. Which is NOT a jQuery utility function?

  • jQuery.each, a general purpose iterator for looping over arrays or objects
  • jQuery.isNumeric, which can check whether its argument is, or looks like, a number
  • jQuery.extend, which can merge objects and make complete deep copies of objects
  • jQuery.isMobile, which can tell whether the user is using a mobile browser

Q39. Given this set of checkboxes, how can you select the ones that have the phrase “sun” as part of the value?

<input type="checkbox" name="artists[]" value="sun-ra">
<input type="checkbox" name="artists[]" value="otis-redding">
<input type="checkbox" name="artists[]" value="captain-beefheart">
<input type="checkbox" name="artists[]" value="king-sunny-ade">
<input type="checkbox" name="artists[]" value="weather-report">
  • $('checkbox').val(/sun/);
  • $('input[value*="sun"]');
  • $('input[value|="sun"]');
  • $('input:checkbox').attr('value', '*sun*');

Q40. How can you get an AJAX request to go through without triggering any of jQuery’s AJAX events?

  • Set the type option to “none”.
  • Set the processData option to false.
  • Set a success callback that returns false.
  • Set the option “global” to false.

Q41. How do you change the current value of a text field with the class .form-item to “555-1212”?

  • $.val('.form-item', '555-1212');
  • $('.form-item').val('555-1212');
  • $('.form-item').data('value', '555-1212');
  • $('.form-item').set('value', '555-1212');

Q42. How would you fire a callback when any AJAX request on a page has completed?

  • $('body').ajaxComplete(function() { console.count('An AJAX request completed'); });
  • $(document).on('ajax-complete', function() { console.count('An AJAX request completed'); });
  • $('body').on('ajaxComplete', function() { console.count('An AJAX request completed'); });
  • $(document).ajaxComplete(function() { console.count('An AJAX request completed'); });

Q43. Given this set of checkboxes, how can you select the one with the value “blimp”?

<input type="checkbox" name="songs[]" value="satisfaction">
<input type="checkbox" name="songs[]" value="respect">
<input type="checkbox" name="songs[]" value="blimp">
<input type="checkbox" name="songs[]" value="saturn">
<input type="checkbox" name="songs[]" value="penguins">
  • $('input[value="blimp"]');
  • $('input[value!="blimp"]');
  • $('checkbox').val('blimp');
  • $('input:checkbox').attr('value', 'blimp');

Q44. Given this snippet of HTML and jQuery code, what does the jQuery do?

<ul class="menu">
  <li><a href="#" class="active">Home</a></li>
  <li><a href="#">Page 2</a></li>
</ul>
<ul class="active submenu">
  <li><a href="#">Subpage 1</a></li>
  <li><a href="#">Subpage 2</a></li>
</ul>
var m = $('.menu'), sm = $('.submenu');
m.add(sm);
m.css('font-weight', 'bold');
  • It makes all the menu items bold.
  • It throws an exception on line 3.
  • It makes the first set of menu items, not the second, bold.
  • It makes the second set of menu items, not the first, bold.

Q45. You want to take a block of type and animate it to a larger size with jQuery. The following HTML and JavaScript behaves strangely. What is the issue?

<div id="type" style="font: 1em/1.5 helvetica, arial, sans-serif; background: #ffc; padding: 0">
  Animate me!
</div>
$('#type').animate({
  fontSize: '+=1em'
}, 3000);
  • jQuery does not support ems and will make the type 1 pixel larger instead of 1 em larger.
  • jQuery cannot override CSS in a style attribute, so the font size will not change.
  • The font size was set with a shorthand property, so jQuery will not animate the font size at all.
  • The font size was set with a shorthand property, so jQuery will start the animation from 0 instead of from 1 em.

Q46. When using the clone() function to duplicate an element, what is one of the main concerns your code needs to watch out for?

  • The clone() function may ignore data attributes on the original elements.
  • The clone() function may result in elements with duplicate ID attributes.
  • The clone() function may remove CSS classes from the cloned elements.
  • The clone() function may not respect the attribute order of the original elements.

Q47. When incorporating a plugin into a project, what are the important steps for basic installation and usage?

  • The jQuery script tag must come first, followed by the plugin, followed by your custom scripts, all preferably at or near the bottom of the page.
  • Your custom scripts must appear first in the document <head>, followed by jQuery, followed by the plugin.
  • The jQuery script tag and the plugin script tag must appear in the document <head>, and your custom scripts can follow anywhere on the page.
  • The jQuery script tag must appear in the document <head>, but the plugin and your custom scripts can appear anywhere else in any order.

Q48. These two script tags show different ways of using jQuery’s ready() method. What is true about both approaches?

<script>
  $(function() {
    // The rest of my code goes here
  });
</script>

<script>
  jQuery(document).ready(function($) {
    // The rest of my code goes here
  });
</script>
  • The code inside them can manipulate the DOM safely, knowing the browser has loaded it fully.
  • The code inside them can manipulate images on the page safely, knowing they have fully downloaded to the browser.
  • The code inside them will be run exactly once per user session.
  • The code inside them is not aware of the DOM.

Q49. Which property of the jQuery event object references the DOM object that dispatched an event?

  • self
  • target
  • object
  • source

Q50. Which describes how jQuery makes working with the DOM faster?

  • jQuery optimizes the DOM in a background thread, making updates faster.
  • jQuery avoids using the DOM at all.
  • jQuery uses a virtual DOM that batches updates, making inserts and deletes faster.
  • jQuery code to perform DOM manipulation is shorter and easier to write, but does not make DOM operations faster.

Q51. There are some issues with this snippet of jQuery. First, it is manipulating CSS directly, rather than manipulating classes and leaving the CSS in stylesheets. What else in this code is best to avoid?

$('.item').css('background-color', 'red');
// some other code here
var firstSubItem = $('.item').find('.sub-item').get(0);
// some other code here too
$('.item').parents('.navigation').css('font-weight', 'bold');
  • The .css() method accepts only an object, not two separate arguments. This will trigger an exception that should be caught.
  • The $('.item') selection is being made several times. This should be cached in a variable for (however slightly) better performance and easier maintainability.
  • The call to .parents() is in an inefficient place.
  • All the calls to $('.item') should be chained together as a single executable line for better performance.

Q52. Which choice is an example of statement chaining?

  • var $p = $('p'); console.log($p.length);
  • $('p').find('a').children('li');
  • $('p > a > li');
  • $('p'); $('a'); $('li');

Q53. How can you ensure that some code executes only when a class active appears on an element?

  • $('.element').attr('class', 'active')
  • $('.element').with('.active')
  • $('.element').hasClass('active')
  • $('.active').then()

Q54. jQuery has a main function for handling AJAX, and several shorthand function including load() that make calling that main function easier. Given this HTML snippet, how can you insert only the second snippet from the source.html file (div#one) into the #load-me div on-demand via AJAX?

<div id="load-me">
  This area will be replaced with AJAX loaded content.
</div>

<div id="one">
  <h1>First Piece</h1>

  <p>
    Lorem ipsum duis maximus quam condimentum dolor eleifend scelerisque.
  </p>
</div>

<div id="two">
  <h1>Second Piece</h1>

  <p>
    Lorem ipsum proin facilisis augue in risus interdum ornare.
  </p>
</div>
  • $('#load-me').get('source.html#one');
  • $('#load-me').get('source.html #one');
  • $('#load-me').load('source.html #one');
  • $('#load-me').load('source.html', '#one');

Q55. Given this HTML list and subsequent two lines of jQuery, what is the difference in the behavior of .closest() and .parents()?

<ul class="items" id="main-menu">
  <li>Item 1 <ul id="sub-menu">
  <li class="leaf">Sub Item 1</li>
  <li>Sub Item 2</li>
  </ul></li>
</ul>
$('.leaf').closest('.items');
$('.leaf').parents('.items');
  • .closest() returns .leaf and #main-menu; .parents() returns #main-menu and #sub-menu.
  • .closest() returns .leaf and #sub-menu; .parents() returns #main-menu and #sub-menu.
  • .closest() returns only #main-menu; .parents() returns #main-menu and #sub-menu.
  • .closest() returns only #sub-menu; .parents() returns #main-menu and #sub-menu.

Q56. What does this line of code do?

$('ul > li:first-child');
  • selects the first list item inside all unordered lists on the page
  • selects the first list item inside the first unordered list on the page
  • selects the first element inside any list items on the page
  • creates a predefined CSS selector that can be reused later

Q57. Below is a list of items that you want to be clickable and an event handler function. How can you assign the event handler to every item in the list in a way that is most performant, and also that ensures that the handler is called even if more items are added to the list programmatically?

<ul class="clickable-list">
  <li>First Item</li>
  <li>Second Item</li>
  <li>Third Item</li>
  <li>Fourth Item</li>
  <li>Fifth Item</li>
</ul>
function listResponder(evt) {
  console.log('You clicked a list item that says', evt.target.innerText);
}
  • $('.clickable-list).click(listResponder);
  • $('.clickable-list).on('click', 'li', listResponder);
  • $('.clickable-list).on('click, append', listResponder);
  • $('.clickable-list).each(function() { $(this).click(listResponder); });
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jQuery CDN

What is CDN?

A content delivery network or content distribution network (CDN) is a distributed system where users can store data and can access cached content. Usually, we store images, Style sheets, Javascript files, etc.

The use of CDN is very efficient when we have to access some static files. It directly connects to our physical server and provides the resources required, because it connects to the proxy server available in the locality and the nearest.

Que: Why we should Use jQuery CDN?

The CDN sends the data from the cache if available. In most of the cases the user has already history and they already have cached the query. When a new website is opened and using the CDN jQuery, CDN refers to the cached file and hence the zero latency is observed.

  1. Removes server Server Delay
  2. Secure and freely available

Must Read: Javascript Interview Questions

Que: How to use jQuery CDN?

As we all know we use CDN a proxy network to store the static files like images, CSS and javascript files. There are two methods that we can choose from to add jQuery in our application. Any of these methods can facilitate jQuery functionality in our application.

1.Hosted jQuery Files:

We can download a jquery file and upload it to our server and we can fetch it in our application. But downloading from their can increase the loading time of our application and It may take more time to produce the first visible snap of page.

2.jQUery CDN

CDN Hosted jQUery is then the solution of the problem in method one. jQuery CDN is the better way to include jQuery functionality in our application. jQuery CDN removes the server latency and TAT i.e. turn around time. Since CDN is a highly equipped Infrastructure, definitely the speed will be considerable.

We can found the Official jQuery CDN here :

The latest stable version: https://code.jquery.com/

There are two ways of including jQuery CDN:

1. jQuery CDN from Google

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

2. jQuery CDN from Google

<script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.3.1.min.js"></script>

I hope you will get to know what is CDN and how it works jQuery. Now you can understand the difference between the hosted jQuery and CDN jQuery.

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What is jQuery

Answers of the question “What is jQuery” is jQuery is a javascript library.

jQuery is written in javascript. It is a library to ease the use of javascript.

A rich library is developed to increase the usability of javascript in common and complex applications.

Javascript provides much functionality to manipulate the HTML DOM tree in the run.

Javascript is a lightweight script and so the jQuery. jQuery is based on javascript functionality.

jQuery simplifies the complex operations done in Javascript like AJAX, animation, DOM traversing and manipulation.

In the go, we can change, load and create HTML DOM and can do actions on them.

So jQuery is a powerful library. jQuery functionality provides a smoother User Experience.  It facilitates a handy tool to the programmers and designers.

The jQuery library has the following important features:

  • jQuery is an OPEN SOURCE
  • It can manipulate HTML/DOM similarly like javascript
  • We can add CSS and styles to HTML using jQuery functionality
  • jQuery handles the HTML event methods like click, hover, change, blur, etc
  • It is easy to manage Effects and animations when we are going with jQuery
  • It simplifies the AJAX request
  • jQuery has vast Utilities like jQuery Mobile, jQuery UI
  • A huge community is available over multiple networks
  • Compatible to almost the browsers

Few useful jQuery Functionality :

show(): display a hidden dom, set a style property display as Block.
hide(): Hide the selector from dom tree, visible on the browser.
animate(): Apply animation effects with selectors.
empty(): Empty the dom and also removes the child elements.
remove(): remove selector dom from tree
removeClass():remove class or classes from selectors
addClass():add class or classes to the selectors
toggleClass():add and remove simultaneously
stop(): stop the propagation of events
fadeIn():hide dom with a fading down effect.
fadeOut():display dom with a fading out effect.

Must Read: jQuery Functionality

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Jquery noConflict() Explained

What is noConflict() method in jQuery?
This is very important to differentiate scripts when we are using many JavaScript framework in our project.As we know jQuery uses dollar symbol ($) as shortcut. There are many other popular frameworks are there as Angular JS,Knockout JS,Kendo JS,Backbone JS,Ember ,Vue etc.
Suppose i one of these frameworks is using the $ symbol as shortcut then one of the scripts either jQuery or the framework implemented parallel may stop working. noConflict is a method to avoid such situation in script.

We can create our self defined symbol or string as shortcut for jQuery. noConflict() return a reference and we can store this reference in a variable.

Example of noConflict() and self defined shortcut:

var jq = $.noConflict();
jq(document).ready(function(){
    jq("button").click(function(){
        jq("p").text("Hi there,Conflict resolved");
    });
});
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jQuery Functionality – Common jQuery Functions

jQuery is a rich library and a very lightweight framework to provide javascript enhanced and modified functionality to our web page. jQuery is a javascript library and written in core javascript concepts. jQuery functionality is basically an easier version of javascript and a simple way to manipulate the DOM in the same way as Java Script does.
This is so popular because it has the number of functions events, chaining properties and they make it convenient as well as easy to use.  The jQuery Functionality provides rapid and smooth actions to perform actions on HTML DOM events.
There are few events and functions which are used frequently in addition to jQuery functionality. We are going to list them here with a one-line explanation. These explanations are very useful when you are explaining jQuery Functionality.
jQuery is a very rich library and has a number of functions. These functions provide a next-gen experience to jQuery functionality.
Find the jQuery functionality of a few popular library methods.
Must Read: What is jQuery?

Find some beautiful functions and their explanations in one line:

show(): display a hidden dom, set a style property display as Block.
hide(): Hide the selector from dom tree, visible on the browser.
animate(): Apply animation effects with selectors.
empty(): Empty the dom and also removes the child elements.
remove(): remove selector dom from tree
removeClass():remove class or classes from selectors
addClass():add class or classes to the selectors
toggleClass():add and remove simultaneously
stop():stop the propagation of event.
fadeIn():hide dom with a fading down effect.
fadeOut():display dom with a fading out effect.
val():get the value of form elements.
text():get the text in dom.
html():get the HTML in dom.
child(): find the child elements in dom.
parent(): find the immediate parent elements of the dom.
parents(): find the parents of the parent of the selector in the dome tree.
siblings(): find the parallel elements in the dom tree.
slideDown(): display the dom with sliding to downwards effect.
slideUp():hide the dome with sliding to up effect.
attr(): get the attribute of DOM.
append(): add the given object to the selector one after one, in a stack style. The object is added as the last child always.
prepend(): add the given object to the selector, but the object is added as the first child always.
after(): add an object just after the selector.
before(): add and object just before the selector.
css(): add some inline css-properties to the selector.
first(): get the first element in the child.
last(): get the last element in the child.
eq(): find the object of equal index passed to it.
noConflict(): avoid conflicts with other javascript frameworks using $ as shortcut symbol.

Conclusion

I Hope these functions will help you in the jquery excercise and application development. They will be helpful to answer your jQuery interview questions. We have added a few of the important functions and these are not the all jQuery functionality. You have to prefer the reference of jQuery to know more about the functions and events. Please share your feedback to improve our articles.
Thanks.
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jQuery Events Frequently asked in various Interviews

Jquery events are attached with some function and function called when event triggers. On a web page actions taken by visitors are events. They can be responded accordingly as click,change,blur,focus,keypress etc. Some common events as categorised as :
Mouse Events : click,dblclick,hover
Keyboard Events : keypress,keydown,keyup
Form Events : change,select,focus,blur
Window : load,scroll,resize

Most Common events and their explanation in one line:

click(): event is triggered when an element is clicked.
change(): event is triggered when the value of a form field is changed.
focus(): event is triggered when a form field is focused.
blur(): event is triggered when a form field is blured.
hover(): event is triggered when moue pointer hover the element.
focusin(): event is triggered when the chield of and element is focused.
focusout(): event is triggered when the chiled of an element is blured.
keydown(): event is triggered when a key from keyboard is pressed down.
keypress(): event is triggered when a key is pressed .keypress event is not fired for ALT, CTRL, SHIFT, ESC.
keyup(): event is triggered when a pressed key is released.
load(): event is triggered when a dom is loaded.
unload(): event is triggered when a dom is unloaded.
mouseenter(): event is triggered when mouse pointer enters the area.
mousedown(): event is triggered when left mouse button is clicked.
mouseout(): event is triggered when mouse pointer leaves the area.
on(): on event is used to add additional handler to dom element.
submit(): event is triggered when form is submitted.
scroll(): event is triggered when the window is scrolled.
select(): event is triggered when the a form element is selected, in combobox or dropdown list.
ready(): event is triggered when the dom is ready and loaded in tree.
resize(): event is triggered when window dimensions are resized.

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Interview Questions on jQuery

What is jQuery?
jQuery is a Javascript library that uses the usage of Javascript very easily. We can handle events, manage CSS properties, DOM element, animation and many more utilities using jQuery library. It is an opensource. It is used by Microsoft, Google, IBM and almost the big players in software industries.

What are selectors?
jQuery selectors are the tool to identify the HTML elements and to manipulate properties. for example:

$(".name") : Class selector
$('#logo') : ID selector
$("button") : tag selector
$(this) : current dom selector

What are the selectors that we use in jQuery?
We use the following selectors in jQuery:
-Tag
-Class
-Id
-all (*)
We can derive more selectors using these main selectors.

What is an event?
An event is a user action. When a user interacts using UI it has to make many clicks, drag, drop, mouse over, change drop-down, keypress actions, these actions are recognized by jQuery.

What are the common events that user make?
Most common events make by users are :
-click
-mouseover
-keypress
-keydown
-change
-input
-drag
-drop
-blur
-dblclick (double click)
-mouseenter

Must Read :

What is toggle()?
toggle() is a function which provides switching functionality between two actions, functions, properties etc. Suppose we can show and hide an element using toggle function.

What is callback?
A callback is a function that is called after when execution finished. We have to specify which function we have to call after a particular execution.

What is alert()?
alert() is used as a callback to show some warning, notification or error.

$("button").click(function(){
        alert("Clicked on button");
});

What is chaining in jQuery?
Chaining is calling of multiple functions in a single statement. for example :

$(".button").css("color", "#ececec").slideUp(1000).slideDown(2000).hide();

How to get value or text of an HTML element?
Since we know jQuery can manipulate HTML DOM, we can use functions to get value, text or html block inside an HTML element. For example

$('.first_name').val();  
//geting value in input box having class as first_name
$('p').html();   //getting html inside a 'p' tag
$('textarea').text();  //getting text inside a textarea

How can we set values for HTML element?
very similar to getting the value, we can set values to elements. For example:

$('.first_name').val('Interview Sortout Blogs');  
//geting value in input box having class as first_name
$('p').html('My blog is based on interview');  
 //getting html inside a 'p' tag
$('textarea').text('This blog is awesome. You are doing a verygood job,Interview Sortout');  //getting text inside a textarea

How to add or remove class from a HTML element?
jQuery have functions to add or to remove classes from an HTML elements. Please see the following examples:

$('button').addClass('btn-danger');
$('button').removeClass('btn-danger');

How to check that an element has a class?
We can use function hasClass().If class found it returns true, other wise returns false.

if($('button').hasClass('btn-danger')){
 alert('Button class is btn-danger');
}

What append() and prepend() functions do?
append() function , adds an HTML block after(at the end) a selector. For example :

$('p').append('Interview Sortout');

prepend() method, adds a block before or at the beginning of the selector. Example:

$('p').prepend('Interview Sortout');

What does parent() method do?
parent() method select the direct parent or immediate ancestor that is next to selector.

What does parents() method do?
parents() select all ancestors , the elements including parent of parent.

What childre() do?
children() method select the immediate child of the selector.

What does find() method do?
find() method search for the selector passed and selects from all the children of selector.

What does siblings() method do?
sibling() method returns all the elements having parralle relationship with selector. We can call them siblings.

How to call AJAX in jQuery?
An AJAX call example in jQuery:

var $post = $.ajax({
  url: "example.php",
  type: "POST",
  data: {id : product_id, product_name:product_name},
  dataType: "json"
});

$post.done(function(msg) {
  $("#log").html( msg );
});

$post.fail(function() {
  alert( "Request failed: Request Has been failed" );
});

 

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