Develop Reference

if one item is clicked, remove the other items?

I'm learning Javascript and jQuery and I'm stuck at this one problem. Let's say my code looks like this:
<div id="hey"> hey </div>
<div id="how"> how </div>
<div id="are"> are </div>
<div id="you"> you </div>
Now, if i click one of the div's, i want the other ones to disappear.
I know, I could create 4 functions for each one of them with on.click hey and display none with how , are and you. But is there a easier way? I bet there is, with classes maybe?
Thanks for responding!

Use siblings to get reference to its "brothers".
Given a jQuery object that represents a set of DOM elements, the .siblings() method allows us to search through the siblings of these elements in the DOM tree and construct a new jQuery object from the matching elements.
$('div').click(function(){
$(this).siblings().hide();
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="hey"> hey </div>
<div id="how"> how </div>
<div id="are"> are </div>
<div id="you"> you </div>
Or you can hide all the other div which not the clicked element using not
Remove elements from the set of matched elements.
$('div').click(function() {
$('div').not(this).hide();
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="hey"> hey </div>
<div id="how"> how </div>
<div id="are"> are </div>
<div id="you"> you </div>

You can just hide siblings() of clicked div.
$('div').click(function() {
$(this).siblings().fadeOut()
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="hey">hey</div>
<div id="how">how</div>
<div id="are">are</div>
<div id="you">you</div>

Yeah there are some easier ways and I could tell a one from it,
Set a common class to all the elements that you are gonna target,
<div class="clickable" id="hey"> hey </div>
<div class="clickable" id="how"> how </div>
<div class="clickable" id="are"> are </div>
<div class="clickable" id="you"> you </div>
And you have to bind a single click event by using a class selector,
$(".clickable").on("click", function(){ });
Now use the .siblings() functions to hide the required elements,
$(".clickable").on("click", function(){
$(this).siblings(".clickable").hide();
});
But using a toggle instead of hide would sounds logical,
$(".clickable").on("click", function(){
$(this).siblings(".clickable").toggle();
});
Since you can do the same operation over all the elements.

You can use not to avoid element and this will indicate current instance.
$(document).ready(function(){
$("div").on("click",function(){
$("div").not(this).hide("slow");
})
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="hey"> hey </div>
<div id="how"> how </div>
<div id="are"> are </div>
<div id="you"> you </div>

Assign a class to each of the elements:
<div id="hey" class='sth'> hey </div>
<div id="how" class='sth'> how </div>
<div id="are" class='sth'> are </div>
<div id="you"class='sth' > you </div>
And write a js function onclick.
Remove class 'sth' from 'this' element in this function
Hide all elements with class 'sth' $('.sth').hide();

For this example - you don't need to add any further selectors to target the div's although in reality - this solution wwould cause all divs on the page to be affectecd - adding classes would be my actual suggestion: - but this works for this example. Click a div and all divs are hidden then the clicked one is shown. I also added a reset button to allow all divs to reappear.
$('div').click(function(){
$('div').hide();
$(this).show();
});
$('#reset').click(function(){
$('div').show();
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="hey"> hey </div>
<div id="how"> how </div>
<div id="are"> are </div>
<div id="you"> you </div>
<hr/>
<button type="button" id="reset">Reset</button>

$(document).ready(function(){
$("div").on("click",function(){
$("div").not(this).toggle("slow");
})
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="hey"> hey </div>
<div id="how"> how </div>
<div id="are"> are </div>
<div id="you"> you </div>

Only show parent if child contains certain string

I have a group of divs that appear on multiple pages, that have this pattern:
<div class=“entry”>
<div id=“post”>
<div class=“text”>
<div class=“service”></div>
<div class=“timeline”>
<div class=“entry-title”>
#hashtagOne
</div>
</div>
</div>
</div>
</div>
<div class=“entry”>
<div id=“post”>
<div class=“text”>
<div class=“service”></div>
<div class=“timeline”>
<div class=“entry-title”>
#hashtagTwo
</div>
</div>
</div>
</div>
</div>
<div class=“entry”>
<div id=“post”>
<div class=“text”>
<div class=“service”></div>
<div class=“timeline”>
<div class=“entry-title”>
#hashtagThree
</div>
</div>
</div>
</div>
</div>
This group appears on multiple pages.
My ideal javascript/jquery solution is something like this:
display:none on all div class="entry"
if child div class="entry-title" contains #something, change parent div class="entry" to display:block
so that on Page One I can insert this code to only show #hashtagOne, on Page Two only #hashtagTwo, etc. etc.

Try something like this:
$('.entry-title').each(function(i,v){
if ($(this).text().trim().charAt(0) =="#") {
$(this).closest('.entry').show();
}
});
https://jsfiddle.net/0ybstx9o/

This simply works fine :
$(document).ready(function(){
$(".entry").each(function(){
if($(this).find(".entry-title:contains('#something')").length > 0){
$(this).css("display","block");
}
});
});

Its pretty simple, just use :contains() and .closest() together either on page load or whatever event you want this display:block behavior to run.
As you want to show based on differnt pages, I suggest to use page title and set it to title="Page One" and title="Page Two" etc and then compare it in document ready state and show accordingly the desired div
jQuery(document).ready(function(){
jQuery('div.entry').hide();
if(jQuery(document).find("title").text() == 'Page One')
{
jQuery( "div.entry-title:contains('#something')" ).closest('.entry').show();
}
else if(jQuery(document).find("title").text() == 'Page Two')
{
jQuery( "div.entry-title:contains('#something Else')" ).closest('.entry').show();
}
});

$(".entry").find(".entry-title").text(function(key, text) {
if (text.indexOf("#")>=0) {
$(this).parents(".entry").hide()
}
})
Here is the working Plunker

jQuery's `.not` not working

I'm accomplishing a collapsible menu in jQuery. After clicking on any header it's next sibling (the box) should be expanded and all other boxes should be collapsed.
HTML
<div class="finbox" id="finbox1">
<div class="finheader" id="finheader1">
<div class="finleft">1. Before you place your order > sign in </div> <div class="finright"> </div>
</div>
<div class="finbody">
</div>
</div>
<div class="finbox" id="finbox2">
<div class="finheader" id="finheader2">
<div class="finleft">2. Delivery Address </div> <div class="finright"> </div>
</div>
<div class="finbody">
</div>
</div>
...
...
...
jQuery
$('.finheader').click(function(e){
$(this).next().slideDown(); // .finbody slide down
$(this).next().addClass('selbdy');
$(this).addClass('finsel');
$('.finbody:not(.selbdy)').slideUp(); // All .finbody except '.selbdy' slide down
console.log('Slide Down');
});

Replace:
$(this).next().addClass('selbdy');
$(this).addClass('finsel');
With:
$('.finbody').removeClass('selbdy');
$(this).next().addClass('selbdy');
$('.finheader').removeClass('finsel');
$(this).addClass('finsel');
The rest of you code looks good and should work fine.

How about this:
$('.finheader').click(function(e){
$('.finbody').slideUp();
$(this).next().slideDown();
console.log('Slide Down');
});
https://jsfiddle.net/28gug87k/

You will find it easier to work from $('.finheader').not(this) .
You also need to remove any 'finsel'/'selbdy' classes previously added.
$('.finheader').click(function(e) {
$(this).addClass('finsel').next().slideDown().addClass('selbdy');
$('.finheader').not(this).removeClass('finsel').next().slideUp().removeClass('selbdy');
});

Add class to the div if div have specific class

Here i am trying to add class alignright in blog-post div if div have the specific class blog-post but bellow code is not working help me to sort out this.
<div class="switches">
<span class="blog off">Blog</span>
</div>
<div class="timeline">
<script>
$(".switches span").click(function(){
$(this).closest("span").toggleClass('off');
if ( $( this ).hasClass( "blog off" ) ) {
$('.timeline').first().removeClass('timeline').
children('div').hasClass('blog-post').addClass('alignright');
}
});
</script>
<div class="single-post single-post blog-post">
<div class="single-post single-post web-post"></div>
</div>
</div>

The .hasClass() function doesn't do what your code thinks it does. It always just returns a boolean. You want .filter():
$('.timeline').first().removeClass('timeline').children('div').filter('.blog-post').addClass('alignright');

<div class="switches">
<span class="blog off">Blog</span>
</div>
<div class="timeline">
<div class="single-post single-post blog-post"></div>
<div class="single-post single-post web-post"></div>
</div>
<script>
$(".switches span").click(function(){
$(this).toggleClass('off');
if ($(this).hasClass("blog off")) {
var mydiv = $(this).parent().next();
mydiv.removeClass('timeline');
mydiv.find('div.blog-post').addClass('alignright');
}
});
</script>

The problem is the hasClass() method, which will return a boolean value, so calling addClass after that it will fail
$(".switches span").click(function () {
//this is the span
$(this).toggleClass('off');
if ($(this).hasClass("off")) {
$(this).next('div.blog-post').addClass('alignright');
}
});

Jquery div expands all divs on page

<script type="text/javascript">
jQuery(document).ready(function() {
jQuery(".content").hide();
jQuery(".link").click(function()
{
jQuery("div.content").slideToggle(500);
});;
});
</script>
How to expand only the div which is linked to the specific link?
Edit:
Its done like this
<div class="comment">
<div class="bar">
<a class="link">#</a>
</div>
</div>
<div class="content">
<div class="comment">
<div class="bar">
<a class="link">#</a>
</div>
</div>
</div>

EDIT 2:
You changed your HTML. Now do this:
jQuery(this).closest('div.comment').next('div.content').slideToggle(500);
But wait! Now you have 2 different div.link elements in different relation to .content elements. Is this your actual HTML markup?
You could also do this:
jQuery(this).closest('div.content').slideToggle(500);
Please provide your actual HTML.
EDIT:
Based on updated question, do this:
jQuery(this).parents('div.blaat1').eq(1).next().slideToggle(500);
How to expand only the div which is linked to the specific link?
How are they linked?
If the div is a descendant, do this:
jQuery(this).find('div.content').slideToggle(500);
If the div is a an ancestor, do this:
jQuery(this).closest('div.content').slideToggle(500);
If the div is the next sibling, do this:
jQuery(this).next().slideToggle(500);
If the div is the previous sibling, do this:
jQuery(this).prev().slideToggle(500);
Without seeing your HTML structure, we can only guess at the solution.

For this HTML:
<div class="blaat1">
<div class="blaat1">
<a class="link">#</a>
</div>
<div class="blaat2">
<a class="link">#</a>
</div
</div>
<div class="content">
<div class="otherdivs">
<div class="blaat1_div"><p>Hi – I'm blaat 1</p></div>
<div class="blaat2_div"><p>Hi – I'm blaat 2</p></div>
</div>
</div>
Use this JS:
<script type="text/javascript">
$(document).ready(function() {
$(".content").hide();
$(".link").click(function() {
var blaat = $(this).parent().attr("class");
$(blaat+"_div").slideToggle(500);
});;
});
</script>
I haven't tested that, but it should work.

Try this:
$(".link").click(function(){
$(this).parents('div.content').slideToggle(500);
});;