jQuery selectors are a critical skill for any front-end developer Mastering how to target and manipulate elements is key to jQuery proficiency.
During jQuery interviews, you can expect several questions probing your selector knowledge. In this article I’ll cover the 20 most common jQuery selector interview questions to help you ace any technical interview.
Let’s dive in!
1. Explain the Different Types of jQuery Selectors
There are several ways to target elements with jQuery selectors:
-
ID Selector – Target an element by its unique ID using the # symbol. For example:
$("#myID"). -
Class Selector – Select elements by a class name using the . symbol. For example:
$(".myClass"). -
Element Selector – Target elements by the element name. For example:
$("div"). -
Universal Selector – Select all elements on a page using the * symbol. For example:
$("*"). -
Attribute Selector – Target elements by an attribute or attribute value. For example:
$("[href]")or$("[href='value']"). -
Pseudo-class Selector – Target elements based on a certain state, like
:hoveror:focus. -
Descendant Selector – Select elements that are descendants of a parent element. For example:
$("ul li"). -
Child Selector – Select direct children of a parent with the > symbol. For example:
$("ul > li").
The key is understanding when to use each selector type depending on the target elements.
2. What is the Difference Between $(“div”) and $(“#myDiv”)?
The element selector $("div") selects all <div> elements on a page. The ID selector $("#myDiv") targets only the single <div> element with the ID value “myDiv”.
Element selectors target all matching elements, while ID selectors pinpoint only the uniquely identified element.
3. When Would You Use a Class Selector vs. ID Selector?
Use class selectors when you want to apply the same styling or behavior to multiple elements. Classes allow reusability across elements.
ID selectors should only be used for unique, single elements that need styled or referenced independently. IDs can only be used once per page.
So for broad reusability, apply classes. For unique identifiers, assign IDs.
4. How Do You Select an Element By Two Classes?
To target elements with multiple classes, chain the class selectors together without spaces.
For example, to select <div class="box red">, you would use:
$(".box.red")Chaining class selectors together allows you to get very specific in your targeting.
5. Explain the Difference Between $(“.box”) and $(“.box”).find(“p”)
$(".box") selects all elements with the class “box”.
$(".box").find("p") first selects all “.box” elements, but then drills down to find only the <p> elements inside those boxes.
So .find() allows you to target child elements within a jQuery object. It only selects descendants of the initially selected elements.
6. What Does the :hidden Selector Allow You To Target?
The :hidden pseudo-class selector allows you to select any hidden elements on the page.
This includes elements with display: none or visibility: hidden set, as well as any elements currently scrolled out of view.
It’s useful for determining if content is hidden and handling those elements accordingly.
7. What’s the Difference Between :first and :first-child Selectors?
:first selects only the first element in the matched selection.
So $(".myClass:first") gets only the first element with “myClass”.
Whereas :first-child targets the first child element within each parent element individually.
So $(".myBox:first-child") selects the first .myBox element within each parent. Subtle but important distinction!
8. How Do You Select Even/Odd Elements in jQuery?
You can use the :odd and :even pseudo-selectors to alternate between elements.
For example, to style odd table rows:
$("tr:odd").css("background", "grey");This provides an easy way to create zebra striping on tables.
You could also select the 4th element using :eq():
$("div:eq(3)").addClass("fourth");9. What’s the Difference Between :eq() and :nth-child()?
:eq(index) selects the element at the specified index within the matched selection. Index starts at 0.
So $("div:eq(2)") selects the third <div> element.
Whereas :nth-child(n) specifically targets the nth child element within the parent.
So $("div:nth-child(2)") selects the second <div> element within each parent.
:eq() works on the selected elements, while :nth-child() operates on all children under the parent.
10. How Do You Select All Checkboxes on a Page That Are Checked?
We can combine the :checkbox selector and :checked pseudo-class:
$(":checkbox:checked")This will select all checked checkbox inputs.
We could also be more specific and use:
$("input[type='checkbox']:checked")Chaining together selectors gives us lots of flexibility in targeting.
11. What’s the Difference Between .parent() and .parents()?
.parent() selects only the direct parent of the selected element.
So $("span").parent() gets the span’s immediate parent.
.parents() goes up multiple levels in the DOM tree and selects all ancestor elements, all the way up to the <html>.
So $("span").parents() selects the span’s parent, grandparent, great-grandparent, etc.
12. How Do You Select All Elements Except For One?
We can use the .not() method to exclude elements from a selection.
For example, to select all paragraphs except the one with ID “intro”:
$("p").not("#intro")This selects all paragraphs on the page besides the one excluded.
13. What’s the Difference Between .prev() and .prevAll()?
.prev() selects only the previous adjacent sibling of an element.
So $("h2").prev() gets the element immediately before <h2>.
.prevAll() selects all previous sibling elements before it.
So $("h2").prevAll() gets all sibling elements before <h2>, not just the one directly before it.
14. How Do You Select All Images that End With “.png”?
We can use the attribute ends with selector:
$('img[src$=".png"]')This targets <img> elements whose src attribute ends with “.png”.
We can also combine attribute selectors:
$('img[src$=".png"][title]')This selects .png images that also have a title attribute. Powerful targeting!
15. How Do You Select All Elements With No Classes or IDs?
To select elements without classes or IDs, we exclude them from the * universal selector:
$("*").not([class]).not([id])First we select all elements, then filter out those with a class attribute or ID attribute.
16. What Selector Targets Links That Start With “https”?
We can use the attribute starts with selector:
$('a[href^="https"]')This selects anchor tags with an href attribute that starts with “https”.
We could also target links ending with “.pdf”:
$('a[href$=".pdf"]') The ^= and $= operators are useful for targeting by partial attributes.
17. How Do You Select All Elements that Have Class “box” Inside Class “container”?
We can chain together descendant selectors:
$(".container .box")This selects all elements with class “box” that are inside an element with class “container”.
Think of it like defining a path to target nested elements.
18. How Do You Select the First 5 <tr> Elements Inside a Table?
We can combine nth-child pseudo selectors with element selectors:
$("tr:Submit an interview question
Questions and answers sent in will be looked over and edited by Toptal, LLC, and may or may not be posted, at their sole discretion.
Toptal sourced essential questions that the best jQuery developers and engineers can answer. Driven from our community, we encourage experts to submit questions and offer feedback.
Explain what the following code will do:
This code runs a query to get any element whose ID comes first, along with all elements whose class comes first and all elements that are children of the element and have a name attribute that ends in “first.” This is an example of using multiple selectors at once. The function will return a jQuery object containing the results of the query. 2 .
These lines of code are for an app that needs to set a click handler for all buttons on the page, even ones that are added dynamically later.
What’s wrong with this code? How can it be fixed so that it works correctly even if buttons are added later on?
The button that is added dynamically after the call to bind() will not have the click handler attached. This is because the bind() method only connects handlers to elements that are already there when it is called.
This issue can be fixed with functions that use “event bubbling” to match events on elements from the present and the future. In the past, this was done by replacing bind() with live(). live() was deprecated in jQuery 1. 7 though. delegate() is like live(), but it lets you choose how far an event must travel through the DOM.
The best way to do it is to use on(), which, depending on its syntax, can act like bind(), live(), or delegate(). The following code attaches the handler to all current and future buttons:
What selector would I use to find all elements whose IDs end in a certain string? How would I change the selector to only find elements whose IDs end in the same string?
Let’s say you want to retrieve all elements whose IDs end with “txtTitle”. This could be done using the following selector:
To retrieve only
elements whose IDs end with “txtTitle”, the selector would be:
Apply to Join Toptals Development Network
and enjoy reliable, steady, remote Freelance jQuery Developer Jobs
What’s the deal with the $ in jQuery? What is it and what does it mean?
Also, how can you use jQuery with another JavaScript library that names things with $? You’ll get extra points if you can give two answers.
Since $ has no special meaning in JavaScript, it is free to be used in object naming. In jQuery, it is simply used as an alias for the jQuery object and jQuery() function.
However, jQuery is not the only one that can use $. There may be times when you want to use it with another JS library that also uses $, which would cause a confusing name issue. jQuery provides the jQuery. noConflict() method for just this reason. After calling this method, you have to use the underlying name jQuery whenever you talk about jQuery and its functions.
Here’s an example from the jQuery documentation:
Alternatively, you can also use a closure instead of the $.noConflict() method; e.g.:
Given the following HTML:
and the following CSS:
Write code in jQuery to animate the #expander div, expanding it from 100 x 100 pixels to 200 x 200 pixels over the course of three seconds.
This could be done in jQuery as follows:
What is method chaining in jQuery? Provide an example.
What advantages does it offer?
It is possible to use method chaining in jQuery to run multiple methods on a jQuery selection in a single code statement. For example, the following snippets of code are equivalent:
Without chaining:
With chaining:
If you don’t use chaining, jQuery has to search the whole DOM to find the button before each method is applied. With chaining, the button only needs to be selected once. Thus, in addition to yielding more concise code, method chaining in jQuery offers a potentially powerful performance advantage.
Note: To be exact, it should be said that jQuery method chaining is not the only way to avoid searching the whole DOM over and over again. One could also set a variable equal to the initial DOM search results (i. e. , in the above example, one could set a variable equal to $( “button#play-movie” and then call the on(), css(), and show() methods on that variable). However, chaining is still the shorter and faster choice, and it doesn’t need to store the result in a local variable. 7 .
Explain what the following code does:
This code uses method chaining to accomplish a couple of things. First, it selects all the elements and changes their CSS width to 300px. In the next step, it adds all the elements to the selection. This lets it change the background color of both the and elements to blue. 8 .
What is the difference between jQuery.get() and jQuery.ajax()?
jQuery. ajax() is the all-encompassing Ajax request method provided by jQuery. It lets you make very specific Ajax requests, with choices for how long to wait for a response, what to do if the request fails, whether it blocks (synchronous) or doesn’t block (asynchronous), what format to ask for the response, and a lot more.
jQuery. get() is a shortcut method that uses jQuery. ajax() under the hood, to create an Ajax request that is typical for simple retrieval of information. Other pre-built Ajax requests are provided by jQuery, such as jQuery. post(), jQuery. getScript(), and jQuery. getJSON(). 9 .
Which of the two lines of code below is more efficient? Explain your answer.
The first line of code, which is pure JavaScript without jQuery, is more efficient and faster. Executing the second line of code, which is jQuery, will trigger a call to the JavaScript version.
This scripting language, JavaScript, is used by jQuery to make working with the document tree (DOM), though it slows things down a bit. It is a good idea to remember that jQuery is not always better than plain old JavaScript. Always consider whether using jQuery really provides a useful advantage for your project. 10 .
Explain and contrast the usage of event.preventDefault() and event.stopPropagation(). Provide an example.
event. stopPropagation() stops an event from bubbling up the event chain, whereas event. The browser’s default action on that event is stopped by preventDefault(), but the event still moves up the event chain.
For example, consider the following code snippet:
When the button is clicked, stopPropagation() is called. This means that the event never gets sent to the div, so its click handler never fires. It effectively stops parent elements from knowing about an event on their children.
If you changed the above call to stopPropagation() to a call to preventDefault(), the div’s click handler would still fire, but the browser’s default action would not happen.
The stopPropagation() and preventDefault() methods are mostly used in jQuery event handling, but they can also be used in plain JavaScript. ) 11 .
If (a) a jQuery event handler, (b) a regular JavaScript onclick event handler for an anchor tag, and (c) a regular JavaScript onclick event handler for a non-anchor tag (e) all return false, what does that mean? g. , a div, button, etc. )?.
(a) Returning false from a jQuery event handler is effectively the same as calling both preventDefault() and stopPropagation() on the passed jQuery event object.
b) If the regular JavaScript onclick event handler for an anchor tag returns false, the browser can’t go to the link address, and the event doesn’t spread through the DOM.
(c) Returning false from a regular JavaScript onclick event handler for a non-anchor tag (e. g. , a div, button, etc. ) has absolutely no effect. 12 .
jQuery provides a useful .clone() method to create a deep copy of matching elements.
Answer the following questions:
- What is meant by a “deep copy”?
- When a copy is made, what is usually left out? How can some of this behavior be controlled?
- What is a potential “gotcha” when using the . clone() method? (HINT: Name an attribute of an element that you do not want to copy.)
The . The clone() method makes a deep copy of the set of matched elements. This means that it copies not only the matched elements but also their child elements and text nodes.
Normally:
- Arrays and objects in element data are not copied; the original element and the cloned element will still share them. You have to copy each file “by hand” if you want to deep copy all of them.
- Any event handlers that are attached to the original element are not copied to the copy.
It’s possible to make copies of all the event handlers that are bound to the new copy of the element by setting the withDataAndEvents parameter to true.
As of jQuery 1. 4, all element data (attached by the . data() method) is also copied to the new copy.
As of jQuery 1. 5, deepWithDataAndEvents can be added to withDataAndEvents if you want to copy the events and data for all children of the cloned element.
Using . Clone() can create elements with duplicate id attributes, which are supposed to be unique. This could be a problem. When cloning an element with an id attribute, it’s important to remember to change the clone’s id before adding it to the DOM. 13 .
Explain the .promise() method in jQuery, including how and why it would be used.
Consider the code snippet below. What is the difference between the start and end times shown if there are 5 things on the page?
The .promise() method returns a dynamically generated Promise that is resolved once all actions of a certain type bound to the collection, queued or not, have ended.
It takes two optional arguments:
- type: The type that is returned by default is “fx,” which means that the promise is resolved when all of the animations for the selected elements are done.
- target – If a target object is specified, . promise() will connect to it and return this object instead of making a new one.
In the code sample provided, the difference between the start and end times displayed will be 10 seconds. This is because . In this case, promise() will wait for all animations (all fadeOut() calls) to finish. The last one will finish 10 seconds after the first one. e. , 5 * 2 seconds) after the animation starts. 14 .
What is the right way to get rid of an element from the DOM in jQuery before its Promise is over?
A returned Promise in jQuery is linked to a Deferred object stored on the .data() for an element. Since the .remove() method removes the element’s data as well as the element itself, it will prevent any of the element’s unresolved Promises from resolving.
Therefore, if it is necessary to remove an element from the DOM before its Promise is resolved, use .detach() instead and follow with .removeData() after resolution. 15 .
Explain the difference between the .detach() and .remove() methods in jQuery.
The .detach() and .remove() methods are the same, except that .detach() retains all jQuery data associated with the removed elements and .remove() does not. .detach() is therefore useful when removed elements may need to be reinserted into the DOM at a later time. 16 .
What’s the difference between document.ready() and window.onload()?
The document. ready() event occurs when all HTML documents have been loaded, but window. onload() occurs when all content (including s) has been loaded. So generally the document. ready() event fires first. 17 .
What’s the difference between prop() and attr()?
You can use both prop() and attr() to get or set the value of a property of an element attribute. However, attr() returns the property’s default value, while prop() returns the property’s current value.
There is more to interviewing than tricky technical questions, so these are intended merely as a guide. Not every good candidate for the job will be able to answer all of them, and answering all of them doesn’t mean they are a good candidate. At the end of the day, hiring remains an art, a science — and a lot of work.
Tired of interviewing candidates? Not sure what to ask to get you a top hire?
Let Toptal find the best people for you.
Our Exclusive Network of jQuery Developers
Looking to land a job as a jQuery Developer?
Let Toptal find the right job for you.
Job Opportunities From Our Network
jQuery | Interview Question | What are various selectors in jQuery ?
What are jQuery interview questions & answers?
A list of top frequently asked jQuery interview questions and answers are given below. 1) What is jQuery? jQuery is a fast, lightweight, feature-rich client-side JavaScript library. It is cross-platform and supports different types of browsers. It has provided a much-needed boost to JavaScript.
What is a jQuery selector?
A jQuery Selector is a function that uses the expressions to find out matching elements from a DOM based on the given criteria. In a simple language, selectors are used to select one or more HTML elements using jQuery. Once an element is selected then we can perform various operations on that selected element.
What selectors does jQuery support?
JQuery supports a wide range of selectors including ID selectors ( #id ), class selectors ( .class ), element selectors ( element ), and more advanced selectors like attribute selectors and pseudo-selectors. 9. How do you perform event binding in JQuery? You can use methods like .click () , .bind () , .on (), etc., to bind events to elements.
What is Dom selector in jQuery?
In JQuery, the this keyword refers to the DOM element that is currently being acted upon in the event handler. It allows you to perform actions on the element without having to reselect it. 7. What are selectors in JQuery? Can you provide some examples? Selectors are patterns used to match DOM elements.
