We Keep Coding

How to replace all id from href?

I have the following markup
<div class = "general">
<div id ="custom"></div>
</div>
How to change id = "custom" in all <div> with class="general" from href on page using jQuery?

You can try this:
$("div.general").each(function() {
$(this).children("div#custom").text($(this).children("a").attr("href"));
});
If I understand you correctly, you want to iterate through all div.generals, and change the text of each child div#custom to the href of the child a.
See a working example on JSfiddle.
Also, another tip is to avoid using multiple elements with the same id. In your code you have a <div> with id="custom". You also say that the div.general appears multiple times — therefore, the id "custom" will appear multiple times. This is bad practice. I suggest that you change id to class.

You need to loop through all div.general and replace the id attribute of div#custom to whatever is there as the anchors href property. The following code will work:
$(".general").each(function(){
$(this).find("#custom").attr("id", $(this).find("a").attr("href").replace("#", ""));
})
Here the .find() will dig out elements from any depth inside the parent. If you are sure about the DOM position of the elements, you can change the .find() to .children()

Getting ALL First links in a specific class

So I know that using "a:first" will get the first link of a page. Lets assume we have the following:
<div class="masterclass">
Link 1
Link 2
</div>
<div class="masterclass">
Link 1
Link 2
</div>
Naturally I can use the following code to get the first "a" of the class "masterclass"
$('.masterclass a:first').click(function() {
alert('yayfirstlink');
});
However I do not understand how to get the first link of every "masterclass"

You need to use find() here because your selector will find all the anchor elements with in .masterclass then filter only the very first one. But when you use .find(), it will find all the .masterclass elements first then will find the first anchor element in each of them.
$('.masterclass').find('a:first').click(function() {
alert('yayfirstlink');
});
or if you are sure that the target element will be the first child of its parent then you can use :first-child
$('.masterclass a:first-child').click(function() {
alert('yayfirstlink');
});

Try this,
var oFirstAnchor = $(".masterclass a:first-child");

$(".masterclass a:first-child") is what you are looking for.
so:
$('.masterclass a:first-child').click(function() {
alert('yayfirstlink');
});

This is how u loop through each of the masterclass and get the first link of it.
i don't know what you want to do with it though so i can only provide this
$(document).ready(function(){
var fields = $('.masterclass a:first-child');
$.each(fields, function(index, val){
alert(index);
});
});
this alerts the current links array index
http://jsfiddle.net/kBd82/6/

I would recommend using the first of type selector for this.
$('.masterclass a:first-of-type')
This way it will always select the first anchor tag in each masterclass div even if you put other things in the div later.
http://api.jquery.com/first-of-type-selector/

jQuery CSS Selector combined with "this"

I'm trying to figure out if something like this would be possible. We are given that HTML structure
<a href='#' class='anyLink'>
<!-- here goes some content-->
<div class='childElement'><!-- here goes some content--></div>
</a>
I am not able to use ID's because there are many links and it's not defined how many more are to come. So my question is, do you guys know a way where I can do something like this :
$('a').on("click",function(e){
$(this +"div").val(); // for example.
});
I want to select a children element of that anchor that has been clicked or want to get the value of the children element. I also don't have any ID's of the children elements and I am trying to select things via CSS Selectors as td:nth-child(4).
Could anybody tell me if this is possible ?

try
$('a').on("click",function(e){
$("div",this).text(); // for example.
});

$('a').on("click",function(e){
$(this).children("div").eq(0).html();
});

You are looking for a function called .children().
But you can also try something like this:
$('a').on('click', function( e ) {
$('div', this).val(); // Each div child of this element
$(this).children('div'); // Each div child of this element
});

How to gain access to an element on the same level in the DOM?

<div id="dad">
<img id="mum">
<input>
</div>
With jQuery, how could i get access to the input element, get is value or set it for example? I can't work out how to access something on the same level.. and i dont want to be using ID's, just parent/child nodes so i can use the code for loads of dad div's
Thanks!

an addition to Zed,
$(this).parent().children('input');
if you give a name to your input field then you can easily select throughout the others,
$(this).parent().children('input[name=my_input]');
then you can give any value as:
$(this).parent().children('input[name=my_input]').val('any value');
Sinan.

var myEl = $("#dad").children(":input");

$(this).parent().children() ?

Try this, to find the first child input element:
jQuery("div").find("input:first")

If i understand question, you would like achieve input from mum leve?
So try $("#mum ~ input")...
BTW, great site to search jquery function by category http://visualjquery.com/ +nice example.

I guess you want to find siblings (node with same depth and same parent and in DOM tree)
$(el).next() - next element (sibling) for all elements in the set
$(el).nextAll - all following siblings
$(el).nextUntil - all following siblings, stop on some condition (not including first "bad match").
Besides, you have next adjacent selector (+) and next sibling selector.
The same about prev, prevAll and prevUntil.
And you even have a siblings method.
Check this out.

How to clear all <div>s’ contents inside a parent <div>?

I have a div <div id="masterdiv"> which has several child <div>s.
Example:
<div id="masterdiv">
<div id="childdiv1" />
<div id="childdiv2" />
<div id="childdiv3" />
</div>
How to clear the contents of all child <div>s inside the master <div> using jQuery?

jQuery's empty() function does just that:
$('#masterdiv').empty();
clears the master div.
$('#masterdiv div').empty();
clears all the child divs, but leaves the master intact.

jQuery('#masterdiv div').html('');

Use jQuery's CSS selector syntax to select all div elements inside the element with id masterdiv. Then call empty() to clear the contents.
$('#masterdiv div').empty();
Using text('') or html('') will cause some string parsing to take place, which generally is a bad idea when working with the DOM. Try and use DOM manipulation methods that do not involve string representations of DOM objects wherever possible.

I know this is a jQuery related question, but I believe someone might get here expecting a pure Javascript solution. So, if you were trying to do this using js, you could use the innerHTML property and set it to an empty string.
document.getElementById('masterdiv').innerHTML = '';

jQuery recommend you use ".empty()",".remove()",".detach()"
if you needed delete all element in element, use this code :
$('#target_id').empty();
if you needed delete all element, Use this code:
$('#target_id').remove();
i and jQuery group not recommend for use SET FUNCTION like .html() .attr() .text() , what is that? it's IF YOU WANT TO SET ANYTHING YOU NEED
ref :https://learn.jquery.com/using-jquery-core/manipulating-elements/

If all the divs inside that masterdiv needs to be cleared, it this.
$('#masterdiv div').html('');
else, you need to iterate on all the div children of #masterdiv, and check if the id starts with childdiv.
$('#masterdiv div').each(
function(element){
if(element.attr('id').substr(0, 8) == "childdiv")
{
element.html('');
}
}
);

The better way is :
$( ".masterdiv" ).empty();

$("#masterdiv div").text("");

$("#masterdiv > *").text("")
or
$("#masterdiv").children().text("")

$('#div_id').empty();
or
$('.div_class').empty();
Works Fine to remove contents inside a div

You can use .empty() function to clear all the child elements
$(document).ready(function () {
$("#button").click(function () {
//only the content inside of the element will be deleted
$("#masterdiv").empty();
});
});
To see the comparison between jquery .empty(), .hide(), .remove() and .detach() follow here http://www.voidtricks.com/jquery-empty-hide-remove-detach/

When you are appending data into div by id using any service or database, first try it empty, like this:
var json = jsonParse(data.d);
$('#divname').empty();

$("#masterdiv div[id^='childdiv']").each(function(el){$(el).empty();});
or
$("#masterdiv").find("div[id^='childdiv']").each(function(el){$(el).empty();});

try them if it help.
$('.div_parent .div_child').empty();
$('#div_parent #div_child').empty();