Develop Reference

Add querySelectorAll to add a class to a button

I'm having difficulty with using Javascript to add a class to a button.
Context: I have multiple cards in an instragram type format with a post and a "like" button. I want to add a class of card__like-button which changes the image to a filled heart but i remembered that querySelector only applies to the first element, instead i tried using querySelectorAll but now the code doesn't apply to anything.
First attemp:
// Controls for active like button
let likeButton = document.querySelector(".card__like-button");
// Event listener for like button click
likeButton.addEventListener("click", likeButtonClick);
// Add class on button click
function likeButtonClick() {
likeButton.classList.toggle("card__like-button_active");
}
Second attemp
// Controls for active like button
let likeButton = document.querySelectorAll(".card__like-button");
// Event listener for like button click
likeButton.addEventListener("click", likeButtonClick);
// Add class on button click
function likeButtonClick() {
likeButton.classList.toggle("card__like-button_active");
}
I created the following codepen to replicate the problem.
I've search on the site, w3schools documentation, etc. and can't seem to find what am I doing wrong.

Because of the document.querySelectorAll method will return an array of NodeList details see here, you cannot directly assign the addEventListener event to a list.
Instead, you have to loop through each element and assign events to it
document.querySelectorAll(".card__like-button").forEach(ele => {
ele.addEventListener("click", likeButtonClick);
});
// Add class on button click
function likeButtonClick() {
this.classList.toggle("card__like-button_active");
}

Try it :
let likeButtons = document.querySelectorAll(".card__like-button");
Array.from(likeButtons).forEach(ele => {
ele.addEventListener("click", likeButtonClick);
});
// Add class on button click
function likeButtonClick() {
this.classList.toggle("card__like-button_active");
}

JQuery - Function applying only for first element with class

I'm trying to update a modal & video attributes on button click.
It works well but the problem is that it only apply this when i click on the first button ( first element with the class videoBtn ), i want it to be applied on all other buttons with the same class
here is my code
$(".videoBtn").click(function(){
$("#video").attr('src',$(".videoBtn").data('src'));
$(".modal").attr('id', $(".videoBtn").data('target').substring(1));
});

You are not using value of currently clicked element, but first with class, you should use $this instead of $('.videoBtn')
$(".videoBtn").click(function(){
$("#video").attr('src',$(this).data('src'));
$(".modal").attr('id', $(this).data('target').substring(1));
});

$(".videoBtn").each(function(){
$(this).on('click', function() {
$("#video").attr('src',$(".videoBtn").data('src'));
$(".modal").attr('id', $(".videoBtn").data('target').substring(1));
})
})

Add class to element when second div has class

I have a Li element (dropdown) that gets an Active class when parent div (button) is clicked. When this element have this class I want to give another div the same class. When the li element (dropdown) is clicked again the active class is removed, I then want to remove the active class on the second div aswell.
What I got so far:
$('document').ready(function() {
if ($('li').hasClass('active')) {
$("#site-overlay").addClass("active");
}
});
This works a bit on the way in console- it gives my second div the correct class. It doesnt work live though, I guess I cant just call it on pageload? It also doesnt remove the class.

$('li').on('click', function(){
if($(this).hasClass('active')) {
$("#site-overlay").addClass("active");
} else {
$("#site-overlay").removeClass("active");
}
});

Your current example is not setting the active class on the LI elements, so nothing happens, but it should work something like this:
$(function () {
$('ul.megamenu > li').on('click', function () {
$("#site-overlay").toggleClass("active", $(this).hasClass('active'));
});
});
toggleClass can take a second boolean parameter that controls turning on/off the class based on a true/false value.
Note: I hacked the following JSFiddle just to show something working (the clicking just toggles the site-overlay state for now):
https://jsfiddle.net/TrueBlueAussie/doxdmxmL/16/

toggleClass on label with checkbox within

I'm trying to add a class using toggleClass to a label when the label is clicked. The trouble I am having is that when I put a checkbox in it, the class only gets added when you click on the checkbox itself and not the text. How can I make it so that it adds the class when the text is clicked as well?
http://jsfiddle.net/p8erw/1/
Here is the code I'm using
$("label").click(function () {
$(this).toggleClass("highlight");
});

Instead of binding to the labels click event, try binding to the checkbox's change event:
$("input[type=checkbox]").on('change', function () {
$(this).parent().toggleClass("highlight");
});
http://jsfiddle.net/p8erw/4/

Try changing click() function to on change event. :)
$("label").on('change',function() {
$(this).toggleClass("highlight");
});

Jquery change CSS class on clicking

I am working on a project i am having some anchors like tab, each have some CSS class, the selected tab have separate css class. I am clicking on tab and i want to change its CSS class to selected css class i have done this functionality but i am having some problems with it is that previously selected tab also having same class, how can i change the previous selected tab to unselected class,Below is my code
$(".btn").each(function ()
{
$(this).click(function () {
$(this).removeClass("course-btn-tab").addClass("course-btn-tab-selected");
});
});
<div class="course-Search-tabs">
A
B
C
D
</div>

You do not need to use each here, on click of element with class btn remove class for all elements with class btn and assign the desired class to current element (referred by $(this)) which is event source. Also I assume you want to remove selected class from previous elements.
$(".btn").click(function () {
if($(this).hasClass("course-btn-tab-selected"))
$(".btn").removeClass("course-btn-tab-selected").addClass("course-btn-tab");
$(this).addClass("course-btn-tab-selected");
});
Edit: You can improve this by hold the last selected element and changing it class if it suits you.
previouslyClicked = $(".btn").eq(0); //Assuming first tab is selected by default
$(".btn").click(function () {
previouslyClicked.removeClass("course-btn-tab-selected").addClass("course-btn-tab");
$(this).addClass("course-btn-tab-selected");
previouslyClicked = $(this);
});

Wrong usage of $.each()
Use this way:
$(".btn").click(function () {
$(".btn").removeClass("course-btn-tab-selected");
$(this).addClass("course-btn-tab-selected");
});

Should do the trick:
$(".btn").click(function () {
$(".course-btn-tab-selected").removeClass("course-btn-tab-selected").addClass('course-btn-tab');
$(this).removeClass('course-btn-tab').addClass("course-btn-tab-selected");
});

There is another way:
$(".btn").click(function (e) {
e.preventDefault();
$(this).siblings().removeClass("course-btn-tab-selected").addClass('course-btn-tab');
$(this).addClass("course-btn-tab-selected");
});

First you need bind a click event to "btn" CSS class using a jQuery selector, this will allow you manipulate all of the buttons at once.
Next find the previously selected button, remove the selected class and add the regular class.
Finally remove the regular class from the clicked button and add the selected class.
$('.btn').bind('click', function () {
var previouslySelectedButton = $('.course-btn-tab-selected');
var selectedButton = $(this);
if (previouslySelectedButton)
previouslySelectedButton.removeClass('course-btn-tab-selected').addClass('course-btn-tab');
selectedButton.removeClass('course-btn-tab').addClass('course-btn-tab-selected');
});
Alternatively here is a working example using your HTML: jsFiddle