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select a string after a substring in an element's class name

I have an element that contains an input text, to get the input text I'm using the jQuery method find.
The input text has a class name like this page-id-x with the x is variable, so I want to select that number after the substring page-id, and this is what I tried :
var id = ui.item.find('input').attr('class').split(/\s+/).filter(function(s){
return s.includes('page-id-');
})[0].split('-')[2];
console.log(id);
I think this code is too complicated, but I couldn't figure out some other way to do it.
If someone knows a better way, I'll be thankful.
Thanks in advance.

I'm going to assume the x part of page-id-x, not the id part, is what varies (since that's what your code assumes).
Another way to do it is with a regular expression, but I'm not sure I'd call it simpler:
var id = ui.item
.find('input')
.attr('class')
.match(/(?:^|\s)page-id-([^- ]+)(?:\s|$)/)[1];
Example:
var ui = {
item: $("#item")
};
var id = ui.item
.find('input')
.attr("class")
.match(/(?:^|\s)page-id-([^- ]+)(?:\s|$)/)[1];
console.log(id);
<div id="item">
<input class="foo page-id-23 bar">
</div>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
The above makes the same assumptions your current code does, which are:
The first input in ui.item is the one you want
It will have the relevant class name
I assume those are okay, as your question is asking for an alternative, suggesting what you have is working.

As you're using jQuery, take a look at this: https://api.jquery.com/category/selectors/attribute-selectors/
For your case, you can use $('[class^="page-id-"'). These types of selectors (listed on the link above) actually work in CSS, too. (At least most should, if not all.)
To get the number after page-id-, my suggestion would be to store that number in some other HTML attribute, like data-pageID="1" or the like.
So you could have:
<div id="page-id-3" data-pageID="3">CONTENT</div>
Then, when you have the DOM element using $('[class^="page-id-"'), you can access that number with .attr('data-pageID').val().

If you can control the HTML markup, instead of using class names, you can use data attributes instead. For example, instead of:
<input class="page-id-1">
You can use:
<input data-page-id="1">
Then jQuery can find this element effortlessly:
$('[data-page-id]').attr('data-page-id')

You can find your element using the *= selector.
let elem = document.querySelector('[class*=page-id-]')
Once you have the element, you can parse the id out:
let [base, id] = elem.className.match(/page-id-(\d+)/)
console.log('page id: %s', id);

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/

javascript variable for jquery script

I dont know Javascript at all, so sorry for asking a question like this...
This is what I have:
$(document).ready(function(){$("#more0").click(function(){$("#update0").slideToggle("normal");});});
$(document).ready(function(){$("#more1").click(function(){$("#update1").slideToggle("normal");});});
$(document).ready(function(){$("#more2").click(function(){$("#update2").slideToggle("normal");});});
$(document).ready(function(){$("#more3").click(function(){$("#update3").slideToggle("normal");});});
$(document).ready(function(){$("#more4").click(function(){$("#update4").slideToggle("normal");});});
$(document).ready(function(){$("#more5").click(function(){$("#update5").slideToggle("normal");});});
$(document).ready(function(){$("#more6").click(function(){$("#update6").slideToggle("normal");});});
$(document).ready(function(){$("#more7").click(function(){$("#update7").slideToggle("normal");});});
$(document).ready(function(){$("#more8").click(function(){$("#update8").slideToggle("normal");});});
$(document).ready(function(){$("#more9").click(function(){$("#update9").slideToggle("normal");});});
$(document).ready(function(){$("#more10").click(function(){$("#update10").slideToggle("normal");});});
And So On.. Until #more30 and #update30...
So... Right now, my pages has 30 lines :)
Is there a way to do it less complicated?
Thanks!

Use attribute selector ^= . The [attribute^=value] selector is used to select elements whose attribute value begins with a specified value.
$(document).ready(function(){
$("[id^='more']").click(function(){
$("#update" + $(this).attr('id').slice(4)).slideToggle("normal");
});
});

Try to use attribute starts with selector to select all the elements having id starts with more , then extract the numerical value from it using the regular expression and concatenate it with update to form the required element's id and proceed,
$(document).ready(function(){
$("[id^='more']").click(function(){
var index = $(this).attr('id').match(/\d+/)[0];
$("#update" + index).slideToggle("normal");
});
});

use attribute start with selector
$(document).ready(function(){
$("[id^='more']").click(function(){
$("[id^='update']").slideToggle("normal");
});
});

//select all elements that contain 'more' in their id attribute.
$('[id^=more]').click(function(){
//get the actual full id of the clicked element.
var thisId = $(this).attr("id");
//get the last 2 characters (the number) from the clicked elem id
var elemNo= thisId.substr(thisId.length-2);
//check if last two chars are actually a number
if(parseInt(elemNo))
{
var updateId = "#update"+elemNo;//combine the "#update" id name with number e.g.5
}
else
{
//if not, then take only the last char
elemNo= thisId.substr(thisId.length-1);
var updateId = "#update"+elemNo;
}
//now use the generate id for the slide element and apply toggle.
$(updateId).slideToggle("normal");
});

Well first of all, you could replace the multiple ready event handler registrations with just one, e.g
$(document).ready(
$("#more0").click(function(){$("#update0").slideToggle("normal");});
//...
);
Then, since your buttons/links has pretty much the same functionality, I would recommend merging these into a single click event handler registration as such:
$(document).ready(
$(".generic-js-hook-class").click(function(){
var toggleContainer = $(this).data('toggleContainer');
$(toggleContainer).slideToggle("normal");
});
);
The above solution uses HTML Data Attributes to store information on which element to toggle and requires you to change the corresponding HTML like so:
<div class=".generic-js-hook-class" data-toggle-container="#relatedContainer">Click me</div>
<div id="relatedContainer>Toggle me</div>

I would recommend you to use Custom Data Attributes (data-*). Here You can store which element to toggle in the data attributes which can be fetched and used latter.
JavaScript, In event-handler you can use .data() to fetch those values.
$(document).ready(function () {
$(".more").click(function () {
$($(this).data('slide')).slideToggle("normal");
});
});
HTML
<div class="more" data-slide="#update1">more1</div>
<div class="more" data-slide="#update2">more2</div>
<div id="update1">update1</div>
<div id="update2">update2</div>
DEMO

I want to check if `id` has no content

I want check between id that get in var span, if empty was between it put css for input but it not work. how can fix it?
var span = '#'+$('.valid').closest('.auto_box').find('span').attr('id');
if ($(span+':empty').length != 0) {
//alert('ok')
(this).closest('.auto_box').find('input').css('background-color','#000');
}
See here my full code: http://jsfiddle.net/Pjqv2/2/

You are using (this) instead of $('.valid') or whatever you meant with it. Also, you are doing this the wrong way; .find('span') returns the jQuery objects set for that span.
You don't need to get it's ID and then check on that ID again. More importantly, your code seems the need to run on multiple instances of .auto_box. For that, you need to iterate on the set found by (".valid").closest(".auto_box"), which you can do with the jQuery .each() (.each() in jQuery docs) like this:
var autoBoxes = $(".valid").closest(".auto_box");
autoBoxes.each(function(){
if ($(this).find("span").is(":empty")) {
$(this).find("input").css("background-color", "#000");
}
});
Your updated jsfiddle with this script: http://jsfiddle.net/dvir_azulay/Pjqv2/4/

Change (this) to $(span). I updated your fiddle to reflect this change.

How to get attributes of container in jquery?

How can I get attributes values from an container using jquery ?
For example:
I have container div as:
<div id = "zone-2fPromotion-2f" class = "promotion">
here how can I get attribute id value using jquery and than how can I trim the value to get component information ?
update : how can i get attribute values ?
UPDATE: If I have multiple components on page with same div information than how would I know what attribute value is for which component ?
Thanks.

First, that seems to be a ridiculously long ID -- I'm sure it could be made much shorter while still retaining its uniqueness.
Anyway, on to the answer: First you need a way of accessing your "container" div. Typically, one might use a class or ID to get an element. For example, you could "select" this div with the following call to jQuery:
var container = jQuery('#zone-3a...'); // Fill in ... with really long ID
But, since you're asking how to retrieve the ID, I'm presuming that selecting it via the ID is not an option. You could also select it using the class, although it's not guarenteed to be the only element on the page with that class:
var container = jQuery('.promotion');
There are other ways to narrow down the search, such as:
jQuery('div.promotion');
jQuery('div.promotion:first');
Once you have a reference to your "container", you can retrieve the ID like so:
container.attr('id'); // => zone-3a...
// or:
container[0].id; // => zone-3a...

So assuming your div looks like this.
<div id="foo"/>
You could get the ID attribute by using the attr method.
$("div").attr("id);
That assumes that you only have one div on the page. Not really sure what component information you are looking to get?

You read node attributes with the attr() method.
var id = $( '.promotion' ).attr( 'id' );
In terms of parsing that ID for any other arbitrary information, I can't say since it looks like you're using some sort of proprietary format of which I have no knowledge.

loop thru and get all divs with the class promotion and get the id of each...
$('div.promotion').each(function(){
var attr = $(this).attr('id'); // or whatever attribute
});
or single
var myDivClass = $('zone-3a-2f-2f-2fPortal-2fPages-2fHome-2fZones-2fLeft-2f-7ccomponent-3a-2f-2f-2fSpm-2fComponents-2fPromotion-2f').attr('class');
or another single
var myDivID = $('.promotion').attr('id');