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Need to add class to div on hover of another div

I have a list of div with the same class. Each div contains other divs, .header, .body, .footer. When I hover on one of the elements inside one div, for example .header, I need to add/remove a class on the another .footer element inside the same div.
The problem is when I hover one .header - I'm adding class to all .footer elements inside all other div's but I need to add new class only to the .footer inside the current div.
$(document).ready(function() {
$('.header').hover(function() {
$('.footer').addClass('active');
}, function() {
$('.footer').removeClass('active');
});
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="list">
<div class="list_item">
<div class="header"></div>
<div class="body"></div>
<div class="footer"></div>
</div>
<div class="list_item">
<div class="header"></div>
<div class="body"></div>
<div class="footer"></div>
</div>
<div class="list_item">
<div class="header"></div>
<div class="body"></div>
<div class="footer"></div>
</div>
</div>

You could use the :hover pseudo in CSS and the general sibling combinator selector ~
.list_item:hover .header:hover ~ .footer {
background: red;
}
<div class="list">
<div class="list_item">
<div class="header">Hover me</div>
<div class="body">B</div>
<div class="footer">F</div>
</div>
<div class="list_item">
<div class="header">Hover me</div>
<div class="body">B</div>
<div class="footer">F</div>
</div>
<div class="list_item">
<div class="header">Hover me</div>
<div class="body">B</div>
<div class="footer">F</div>
</div>
</div>
otherwise, if you cannot rely on .footer being a next sibling - use jQuery
jQuery(function($) {
$('.header').hover(function() {
$(this).closest('.list_item').find('.footer').toggleClass('active');
});
});
.active {
background: red;
}
<div class="list">
<div class="list_item">
<div class="header">Hover me</div>
<div class="body">B</div>
<div class="footer">F</div>
</div>
<div class="list_item">
<div class="header">Hover me</div>
<div class="body">B</div>
<div class="footer">F</div>
</div>
<div class="list_item">
<div class="header">Hover me</div>
<div class="body">B</div>
<div class="footer">F</div>
</div>
</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

You should be doing it relative to this (which is the current hovered header) and you can use nextAll if that is the only footer in the grouping:
$('.header').hover(function() {
$(this).nextAll('.footer').addClass('active');
},
function() {
$(this).nextAll('.footer').removeClass('active');
});
.active {
color: red;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="list">
<div class="list_item">
<div class="header"> header </div>
<div class="body"> body </div>
<div class="footer"> footer </div>
</div>
<div class="list_item">
<div class="header"> header </div>
<div class="body"> body </div>
<div class="footer"> footer </div>
</div>
<div class="list_item">
<div class="header"> header </div>
<div class="body"> body </div>
<div class="footer"> footer </div>
</div>
</div>

Yes can try below code snippet, I have tested it already.
$(document).ready(function() {
$('.header').hover(function(){
$(this).siblings(".footer").addClass('active');
},
function(){
$(this).siblings(".footer").removeClass('active');
});
});

You need to add different ID property all some div, get $('#footer3') and change it

How can I loop through three div boxes at the time

I have a list of 12 posts wrapped in a div tag and the structure looks like this:
<div class="row">
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
</div>
Is there a way I can loop every third div with the class of content in another div tag?
At the end I would have my structure like this:
<div class="row">
<div class="wrapper">
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
</div>
<div class="wrapper">
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
</div>
<div class="wrapper">
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
</div>
<div class="wrapper">
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
</div>
</div>
Is there a way I can loop every third div with the class of content in another div tag?

You can do something like this
// get all element at position 1,4,7,...etc and iterate
$('.row .content:nth-child(3n + 1)').each(function() {
$(this)
// get all siblings next to it
.nextAll('.content')
// get only next 2 elements from it
.slice(0, 2)
// combine the current element with it
.add(this)
// wrap all elemnts with the div(3 divs)
.wrapAll('<div class="wrapper">')
})
$('.row .content:nth-child(3n + 1)').each(function() {
$(this).nextAll('.content').slice(0, 2).add(this).wrapAll('<div class="wrapper">')
})
console.log($('.row')[0].outerHTML)
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="row">
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
</div>
Or you can use jQuery :lt() pseudo-class selector to avoid slice() method.
$('.row .content:nth-child(3n + 1)').each(function() {
$(this).nextAll('.content:lt(2)').add(this).wrapAll('<div class="wrapper">')
})
$('.row .content:nth-child(3n + 1)').each(function() {
$(this).nextAll('.content:lt(2)').add(this).wrapAll('<div class="wrapper">')
})
console.log($('.row')[0].outerHTML)
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="row">
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
</div>

Loop through the children, every third child create a new wrapper and add each child in the respective wrapper.
var test = document.querySelector("#test");
var index = 2;
for (var child of test.querySelectorAll(".content")) {
if (index++ >= 2) {
var newWrapper = test.appendChild(document.createElement("div"));
newWrapper.className = "wrapper";
index = 0;
}
test.removeChild(child);
newWrapper.appendChild(child);
}
console.log(test.innerHTML);
<div class="row" id="test">
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
<div class="content">
</div>
</div>

Try this
function WrapUpAllDivs(){
var CurrentDivs = $(".row",".content");
for(var i = 0; i < CurrentDivs.length -1 ; i+=3) {
CurrentDivs
.slice(i, i+3)
.wrapAll("<div class=\"wrapper\"></div>");
}
}

Hide an element in DOM when specific class included

I need to hide a div from DOM when specific class included in middle of the html code. Please take a look at this example.
<body>
<div class="first-group">
<h1>Hello world</h1>
</div>
<div class="wrapper">
<div class="second-group">
<div class="main">
<div class="small">
<span class="text-block">Hello mars</span>
</div>
</div>
</div>
</div>
</body>
I tried to achieve this with jQuery .closest() but no luck.
$( ".text-block" ).closest( ".first-group" ).css( "color", "red" );
Any solution?

if($(".second-group span").hasClass("text-block")) {
$('.first-group').css('display', "none");
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<body>
<div class="first-group">
<h1>Hello world</h1>
</div>
<div class="wrapper">
<div class="second-group">
<div class="main">
<div class="small">
<span class="text-block">Hello mars</span>
</div>
</div>
</div>
</div>
</body>

Simply if the length of .text-block inside the wrapper is greater then 0 then simply make .first-group display: none.
if($( ".wrapper" ).find( ".text-block" ).length > 0){
$('.first-group').css( "display", "none" )
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="first-group">
<h1>Hello world</h1>
</div>
<div class="wrapper">
<div class="second-group">
<div class="main">
<div class="small">
<span class="text-block">Hello mars</span>
</div>
</div>
</div>
</div>
If you have multiple .first-group and .wrapper then you can simply loop the wrapper and find its parent and previous element of that parent.
$( ".wrapper" ).find( ".text-block" ).each(function() {
$(this).parents('.wrapper').prev('.first-group').css( "display", "none" );
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="first-group">
<h1>Hello world</h1>
</div>
<div class="wrapper">
<div class="second-group">
<div class="main">
<div class="small">
<span class="text-block">Hello mars</span>
</div>
</div>
</div>
</div>
<div class="first-group">
<h1>Hello world</h1>
</div>
<div class="wrapper">
<div class="second-group">
<div class="main">
<div class="small">
<span class="text-block">Hello mars</span>
</div>
</div>
</div>
</div>

You can try with parents() and siblings() like the following:
$(".text-block").parents('.wrapper').siblings('.first-group').css( "color", "red" );
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<body>
<div class="first-group">
<h1>Hello world</h1>
</div>
<div class="wrapper">
<div class="second-group">
<div class="main">
<div class="small">
<span class="text-block">Hello mars</span>
</div>
</div>
</div>
</div>
</body>

The use of closest will only look for its ancestor, while .first-group is outside the .wrapper div.
In the below code, we are finding the ancestor of the element and then use prev() to get previous element with class .first-group
$(this).closest("div.wrapper").prev(".first-group").css('display', 'none');
See if it works.

Your basic problem is that closest() looks for an ancestor. .text-block is not a descendant of .first-group . Use prev() to find the previous sibling of the containing block.
In response to your comment prevAll works if there are intermediate siblings. I've added a few empty divs to the example to demonstrate. I need to check some fringe cases.
To get this a bit more robust I've used prevUntil to limit the sibling selection combined with prev to find the actual element of interest.
$( ".text-block" ).closest( ".wrapper" ).prevUntil(".first-group").prev().hide();
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<body>
<!-- This Won't Show -->
<div class="first-group">
<h1>Hello world</h1>
</div>
<div></div><div></div>
<div class="wrapper">
<div class="second-group">
<div class="main">
<div class="small">
<span class="text-block">Hello mars</span>
</div>
</div>
</div>
</div>
<!--This Will Show-->
<div class="first-group">
<h1>Hello world, Again</h1>
</div>
<div></div><div></div>
<div class="wrapper">
<div class="second-group">
<div class="main">
<div class="small">
<span class="not-text-block">Hello jupiter</span>
</div>
</div>
</div>
</div>
<!-- This Won't Show -->
<div class="first-group">
<h1>Hello world</h1>
</div>
<div></div><div></div>
<div class="wrapper">
<div class="second-group">
<div class="main">
<div class="small">
<span class="text-block">Hello mars</span>
</div>
</div>
</div>
</div>
<!--This Will Show-->
<div class="first-group">
<h1>Hello world, Again</h1>
</div>
<div></div><div></div>
<div class="wrapper">
<div class="second-group">
<div class="main">
<div class="small">
<span class="not-text-block">Hello jupiter</span>
</div>
</div>
</div>
</div>
</body>
NOTE this will break if you change your HTML structure.

jQuery Toggle closest info

I have the following html:
<div class="col-md-12">
<div class="group">
<div class="label">
<li class="interrogation">?</li>
</div>
</div>
<div class="message"></div>
</div>
<div class="col-md-12">
<div class="group">
<div class="label">
<li class="interrogation">?</li>
</div>
</div>
<div class="message"></div>
</div>
This is my ns.init function:
ns.init = function() {
$(".message").hide();
$(".interrogation").click(function(){
$(".interrogation").closest(".group").parent().find(".message").toggle();
});
}
The current code works but it toggles all the messages on the page when I click one of them. How can I make it toggle only the message that is exactly after the question mark ?

That is because you use $(".interrogation") selector in your function. This selects all elements with that class in the document. Use $(this) to only have the element that you clicked on as reference for your selector.
Here is a working fiddle:
$(function() {
$(".message").hide();
$(".interrogation").click(function(){
$(this).closest(".group").parent().find(".message").toggle();
});
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="col-md-12">
<div class="group">
<div class="label">
<li class="interrogation">?</li>
</div>
</div>
<div class="message">Message1</div>
</div>
<div class="col-md-12">
<div class="group">
<div class="label">
<li class="interrogation">?</li>
</div>
</div>
<div class="message">Message2</div>
</div>

Here you go with a solution https://jsfiddle.net/denquhL1/1/
$('.interrogation').click(function(){
$(this).closest('div.group').next('div.message').slideToggle();
});
.message{
display: none;
}
.interrogation {
cursor: pointer;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="col-md-12">
<div class="group">
<div class="label">
<li class="interrogation">?</li>
</div>
</div>
<div class="message">Message 1</div>
</div>
<div class="col-md-12">
<div class="group">
<div class="label">
<li class="interrogation">?</li>
</div>
</div>
<div class="message">Message 2</div>
</div>
Onclick of .interrogation class, it will traverse to closest .group container, then it will look for next .message container.
Instead of toggle, I've used slideToggle with animation.
Hope this will help you.

Something like this?
var ns = {};
ns.init = function() {
$(".message").hide()
$(".interrogation").click(function() {
var commonParent = $(this).closest(".col-md-12");
commonParent.find(".message").toggle();
});
}
ns.init();
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="col-md-12">
<div class="group">
<div class="label">
<li class="interrogation">?</li>
</div>
</div>
<div class="message">Msg 1</div>
</div>
<div class="col-md-12">
<div class="group">
<div class="label">
<li class="interrogation">?</li>
</div>
</div>
<div class="message">Msg 2</div>
</div>

Hide Parent Div if nested div is empty

I'm trying to hide the outer div when a nested div is empty (including white-space node). I've found a solution that works if there is NO whitespace:
Hide parent DIV if <li> is Empty
I need it to work when there IS white space present, ie:
<div class="gen-customer">
<div class="wrapper">
<div class="heading">Hidden if working 1</div>
<div class="content">
<div class="product"> </div>
</div>
</div>
</div>
Example fiddle

Working fiddle
You could use the both :empty and :contain() selector :
$("div.product:contains(' '), div.product:empty").closest('div.wrapper').hide();
Hope this helps.
$("div.product:contains(' '), div.product:empty").closest('div.wrapper').hide()
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="gen-customer">
<div class="wrapper">
<div class="heading">Hidden if working 1</div>
<div class="content">
<div class="product"> </div>
</div>
</div>
</div>
<div class="gen-customer">
<div class="wrapper">
<div class="heading">Visible if working 2</div>
<div class="content">
<div class="product">text</div>
</div>
</div>
</div>
<div class="gen-customer">
<div class="wrapper">
<div class="heading">Hidden if working 3</div>
<div class="content">
<div class="product"></div>
</div>
</div>
</div>

You can iterate over each div.product and trim the text to remove whitespace. If there's anything left, show it, otherwise, hide its wrapper.
$("div.product").each(function() {
if ($(this).text().trim() == '') {
$(this).closest('div.wrapper').hide()
}
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="gen-customer">
<div class="wrapper">
<div class="heading">Hidden if working 1</div>
<div class="content">
<div class="product"></div>
</div>
</div>
</div>
<div class="gen-customer">
<div class="wrapper">
<div class="heading">Visible if working 2</div>
<div class="content">
<div class="product">text</div>
</div>
</div>
</div>
<div class="gen-customer">
<div class="wrapper">
<div class="heading">Hidden if working 3</div>
<div class="content">
<div class="product"></div>
</div>
</div>
</div>

//Try this using Jquery
<script>
//A perfect reference in Jquery...
var element=$('#target_child');
if($(element).html()==''){
$(element).parent().hide()
}else{
//do some work
}
</script>