Develop Reference

Replace a style value in javascript

I am looking to change a value in a tag with js.
<div class="class1" style="background-image:url(https://www.awebsite.com/sites/default/files/a_image.jpg?t=1529620960)"></div>
I want to change this :
https://www.awebsite.com/sites/default/files/a_image.jpg?t=1529620960`
to this:
https://hello.com/an-other-image.jpg
Thanks !

You can use document.querySelector to get a reference to the <div> element and then update it's style attributes.
// querySelector can use CSS selectors to find the element in the document
// note: this is assuming there is only 1 element on page with this class
var myDiv = document.querySelector('.class1');
// Style properties generally match CSS but camel cased
myDiv.style.backgroundImage = 'url("https://hello.com/an-other-image.jpg")';
You may want to consider adding an id in which case you can use an ID selector or document.getElementById.
If there are multiple elements you want to update, you can use document.querySelectorAll which will return an array of matches which you can loop over and change.
function changeToAnotherBgImage(element) {
element.style.backgroundImage = 'url("https://hello.com/an-other-image.jpg")';
}
// Plenty of alternate ways of writing, arrow function may be appropriate
document.querySelectorAll('.class1').forEach(changeToAnotherBgImage);

You can do something like:
c = document.getElementsByClassName('class1');
for(i = 0; i < c.length; i++){
c[i].style.backgroundImage = 'url(https://hello.com/an-other-image.jpg)';
}

You can do that:
const eleDiv =document.querySelector('.class').style.background = "url('your imge') no-repeat";

Pure JS equivalent of Jquery eq()

What is the pure equivalent of jquery's eq(). For example, how may I achieve
$(".class1.class2").eq(0).text(1254);
in pure javascript?

To get the element index in the array you can use [] in javascript. So to reproduce your code you can use this:
document.querySelectorAll('.class1.class2')[0].textContent = 1254;
or
document.querySelectorAll('.class1.class2')[0].innerHTML = 1254;
In your example 1254 is a number, if you have a string you should use = 'string'; with quotes.
If you are only looking for one/the first element you can use just .querySelector() insteal of .querySelectorAll().
Demo here
More reading:
MDN: textContent
MDN: innerHTML
MDN: querySelectorAll

querySelectorAll returns an array, so you can get the element 0 using index
document.querySelectorAll(".class1.class2")[0].innerHTML = 1254

Here's one way to achieve it. Tested working! It splits up the string you want to select into the parts before the :eq and after the :eq, and then runs them separately. It repeats until there's no more :eq left.
var querySelectorAllWithEq = function(selector, document) {
var remainingSelector = selector;
var baseElement = document;
var firstEqIndex = remainingSelector.indexOf(':eq(');
while (firstEqIndex !== -1) {
var leftSelector = remainingSelector.substring(0, firstEqIndex);
var rightBracketIndex = remainingSelector.indexOf(')', firstEqIndex);
var eqNum = remainingSelector.substring(firstEqIndex + 4, rightBracketIndex);
eqNum = parseInt(eqNum, 10);
var selectedElements = baseElement.querySelectorAll(leftSelector);
if (eqNum >= selectedElements.length) {
return [];
}
baseElement = selectedElements[eqNum];
remainingSelector = remainingSelector.substring(rightBracketIndex + 1).trim();
// Note - for now we just ignore direct descendants:
// 'a:eq(0) > i' gets transformed into 'a:eq(0) i'; we could maybe use :scope
// to fix this later but support is iffy
if (remainingSelector.charAt(0) === '>') {
remainingSelector = remainingSelector.substring(1).trim();
}
firstEqIndex = remainingSelector.indexOf(':eq(');
}
if (remainingSelector !== '') {
return Array.from(baseElement.querySelectorAll(remainingSelector));
}
return [baseElement];
};

document.querySelectorAll(".class1.class2")[0].innerHTML = '1254';

Element.querySelectorAll
Summary
Returns a non-live NodeList of all elements descended from the element on which it is invoked that match the specified group of CSS selectors.
Syntax
elementList = baseElement.querySelectorAll(selectors);
https://developer.mozilla.org/en-US/docs/Web/API/Element.querySelectorAll

Since you're only getting the first one, document.querySelector(".class1.class2") will suffice. It returns the element itself, and doesn't have to build an entire node list just to get the first.
However, if you want anything other than the first, then you will need querySelectorAll.

document.getElementsByClassName exact match to class

There are two similar classes - 'item' and 'item one'
When I use document.getElementsByClassName('item') it returns all elements that match both classes above.
How I can get elements with 'item' class only?

The classname item one means the element has class item and class one.
So, when you do document.getElementsByClassName('item'), it returns that element too.
You should do something like this to select the elements with only the class item:
e = document.getElementsByClassName('item');
for(var i = 0; i < e.length; i++) {
// Only if there is only single class
if(e[i].className == 'item') {
// Do something with the element e[i]
alert(e[i].className);
}
}
This will check that the elements have only class item.
Live Demo

document.querySelectorAll('.item:not(.one)');
(see querySelectorAll)
The other way is to loop over the what document.getElementsByClassName('item') returns, and check if the one class is present (or not):
if(element.classList.contains('one')){
...
}

You're going to want to make your own function for exact matches, because spaces in a class means it has multiple classes. Something like:
function GetElementsByExactClassName(someclass) {
var i, length, elementlist, data = [];
// Get the list from the browser
elementlist = document.getElementsByClassName(someclass);
if (!elementlist || !(length = elementlist.length))
return [];
// Limit by elements with that specific class name only
for (i = 0; i < length; i++) {
if (elementlist[i].className == someclass)
data.push(elementlist[i]);
}
// Return the result
return data;
} // GetElementsByExactClassName

You can use Array.filter to filter the matched set to be only those with class test:
var elems = Array.filter( document.getElementsByClassName('test'), function(el){
return !!el.className.match(/\s*test\s*/);
});
Or only those with test but not one:
var elems = Array.filter( document.getElementsByClassName('test'), function(el){
return el.className.indexOf('one') < 0;
});
(Array.filter may work differently depending on your browser, and is not available in older browsers.) For best browser compatibility, jQuery would be excellent for this: $('.test:not(.one)')

If you have jQuery, it can be done using the attribute equals selector syntax like this: $('[class="item"]').
If you insist on using document.getElementsByClassName, see the other answers.

GetElementByID - Multiple IDs

doStuff(document.getElementById("myCircle1" "myCircle2" "myCircle3" "myCircle4"));
This doesn't work, so do I need a comma or semi-colon to make this work?

document.getElementById() only supports one name at a time and only returns a single node not an array of nodes. You have several different options:
You could implement your own function that takes multiple ids and returns multiple elements.
You could use document.querySelectorAll() that allows you to specify multiple ids in a CSS selector string .
You could put a common class names on all those nodes and use document.getElementsByClassName() with a single class name.
Examples of each option:
doStuff(document.querySelectorAll("#myCircle1, #myCircle2, #myCircle3, #myCircle4"));
or:
// put a common class on each object
doStuff(document.getElementsByClassName("circles"));
or:
function getElementsById(ids) {
var idList = ids.split(" ");
var results = [], item;
for (var i = 0; i < idList.length; i++) {
item = document.getElementById(idList[i]);
if (item) {
results.push(item);
}
}
return(results);
}
doStuff(getElementsById("myCircle1 myCircle2 myCircle3 myCircle4"));

This will not work, getElementById will query only one element by time.
You can use document.querySelectorAll("#myCircle1, #myCircle2") for querying more then one element.
ES6 or newer
With the new version of the JavaScript, you can also convert the results into an array to easily transverse it.
Example:
const elementsList = document.querySelectorAll("#myCircle1, #myCircle2");
const elementsArray = [...elementsList];
// Now you can use cool array prototypes
elementsArray.forEach(element => {
console.log(element);
});
How to query a list of IDs in ES6
Another easy way if you have an array of IDs is to use the language to build your query, example:
const ids = ['myCircle1', 'myCircle2', 'myCircle3'];
const elements = document.querySelectorAll(ids.map(id => `#${id}`).join(', '));

No, it won't work.
document.getElementById() method accepts only one argument.
However, you may always set classes to the elements and use getElementsByClassName() instead. Another option for modern browsers is to use querySelectorAll() method:
document.querySelectorAll("#myCircle1, #myCircle2, #myCircle3, #myCircle4");

I suggest using ES5 array methods:
["myCircle1","myCircle2","myCircle3","myCircle4"] // Array of IDs
.map(document.getElementById, document) // Array of elements
.forEach(doStuff);
Then doStuff will be called once for each element, and will receive 3 arguments: the element, the index of the element inside the array of elements, and the array of elements.

getElementByID is exactly that - get an element by id.
Maybe you want to give those elements a circle class and getElementsByClassName

document.getElementById() only takes one argument. You can give them a class name and use getElementsByClassName() .

Dunno if something like this works in js, in PHP and Python which i use quite often it is possible.
Maybe just use for loop like:
function doStuff(){
for(i=1; i<=4; i++){
var i = document.getElementById("myCiricle"+i);
}
}

Vulgo has the right idea on this thread. I believe his solution is the easiest of the bunch, although his answer could have been a little more in-depth. Here is something that worked for me. I have provided an example.
<h1 id="hello1">Hello World</h1>
<h2 id="hello2">Random</h2>
<button id="click">Click To Hide</button>
<script>
document.getElementById('click').addEventListener('click', function(){
doStuff();
});
function doStuff() {
for(var i=1; i<=2; i++){
var el = document.getElementById("hello" + i);
el.style.display = 'none';
}
}
</script>
Obviously just change the integers in the for loop to account for however many elements you are targeting, which in this example was 2.

The best way to do it, is to define a function, and pass it a parameter of the ID's name that you want to grab from the DOM, then every time you want to grab an ID and store it inside an array, then you can call the function
<p id="testing">Demo test!</p>
function grabbingId(element){
var storeId = document.getElementById(element);
return storeId;
}
grabbingId("testing").syle.color = "red";

You can use something like this whit array and for loop.
<p id='fisrt'>??????</p>
<p id='second'>??????</p>
<p id='third'>??????</p>
<p id='forth'>??????</p>
<p id='fifth'>??????</p>
<button id="change" onclick="changeColor()">color red</button>
<script>
var ids = ['fisrt','second','third','forth','fifth'];
function changeColor() {
for (var i = 0; i < ids.length; i++) {
document.getElementById(ids[i]).style.color='red';
}
}
</script>

For me worked flawles something like this
doStuff(
document.getElementById("myCircle1") ,
document.getElementById("myCircle2") ,
document.getElementById("myCircle3") ,
document.getElementById("myCircle4")
);

Use jQuery or similar to get access to the collection of elements in only one sentence. Of course, you need to put something like this in your html's "head" section:
<script type='text/javascript' src='url/to/my/jquery.1.xx.yy.js' ...>
So here is the magic:
.- First of all let's supose that you have some divs with IDs as you wrote, i.e.,
...some html...
<div id='MyCircle1'>some_inner_html_tags</div>
...more html...
<div id='MyCircle2'>more_html_tags_here</div>
...blabla...
<div id='MyCircleN'>more_and_more_tags_again</div>
...zzz...
.- With this 'spell' jQuery will return a collection of objects representing all div elements with IDs containing the entire string "myCircle" anywhere:
$("div[id*='myCircle']")
This is all! Note that you get rid of details like the numeric suffix, that you can manipulate all the divs in a single sentence, animate them... Voilá!
$("div[id*='myCircle']").addClass("myCircleDivClass").hide().fadeIn(1000);
Prove this in your browser's script console (press F12) right now!

As stated by jfriend00,
document.getElementById() only supports one name at a time and only returns a single node not an array of nodes.
However, here's some example code I created which you can give one or a comma separated list of id's. It will give you one or many elements in an array. If there are any errors, it will return an array with an Error as the only entry.
function safelyGetElementsByIds(ids){
if(typeof ids !== 'string') return new Error('ids must be a comma seperated string of ids or a single id string');
ids = ids.split(",");
let elements = [];
for(let i=0, len = ids.length; i<len; i++){
const currId = ids[i];
const currElement = (document.getElementById(currId) || new Error(currId + ' is not an HTML Element'));
if(currElement instanceof Error) return [currElement];
elements.push(currElement);
};
return elements;
}
safelyGetElementsByIds('realId1'); //returns [<HTML Element>]
safelyGetElementsByIds('fakeId1'); //returns [Error : fakeId1 is not an HTML Element]
safelyGetElementsByIds('realId1', 'realId2', 'realId3'); //returns [<HTML Element>,<HTML Element>,<HTML Element>]
safelyGetElementsByIds('realId1', 'realId2', 'fakeId3'); //returns [Error : fakeId3 is not an HTML Element]

If, like me, you want to create an or-like construction, where either of the elements is available on the page, you could use querySelector. querySelector tries locating the first id in the list, and if it can't be found continues to the next until it finds an element.
The difference with querySelectorAll is that it only finds a single element, so looping is not necessary.
document.querySelector('#myCircle1, #myCircle2, #myCircle3, #myCircle4');

here is the solution
if (
document.getElementById('73536573').value != '' &&
document.getElementById('1081743273').value != '' &&
document.getElementById('357118391').value != '' &&
document.getElementById('1238321094').value != '' &&
document.getElementById('1118122010').value != ''
) {
code
}

You can do it with document.getElementByID Here is how.
function dostuff (var here) {
if(add statment here) {
document.getElementById('First ID'));
document.getElementById('Second ID'));
}
}
There you go! xD

Javascript getElementById based on a partial string

I need to get the ID of an element but the value is dynamic with only the beginning of it is the same always.
Heres a snippet of the code.
<form class="form-poll" id="poll-1225962377536" action="/cs/Satellite">
The ID always starts with poll- then the numbers are dynamic.
How can I get the ID using just JavaScript and not jQuery?

You can use the querySelector for that:
document.querySelector('[id^="poll-"]').id;
The selector means: get an element where the attribute [id] begins with the string "poll-".
^ matches the start
* matches any position
$ matches the end
jsfiddle

Try this.
function getElementsByIdStartsWith(container, selectorTag, prefix) {
var items = [];
var myPosts = document.getElementById(container).getElementsByTagName(selectorTag);
for (var i = 0; i < myPosts.length; i++) {
//omitting undefined null check for brevity
if (myPosts[i].id.lastIndexOf(prefix, 0) === 0) {
items.push(myPosts[i]);
}
}
return items;
}
Sample HTML Markup.
<div id="posts">
<div id="post-1">post 1</div>
<div id="post-12">post 12</div>
<div id="post-123">post 123</div>
<div id="pst-123">post 123</div>
</div>
Call it like
var postedOnes = getElementsByIdStartsWith("posts", "div", "post-");
Demo here: http://jsfiddle.net/naveen/P4cFu/

querySelectorAll with modern enumeration
polls = document.querySelectorAll('[id ^= "poll-"]');
Array.prototype.forEach.call(polls, callback);
function callback(element, iterator) {
console.log(iterator, element.id);
}
The first line selects all elements in which id starts ^= with the string poll-.
The second line evokes the enumeration and a callback function.

Given that what you want is to determine the full id of the element based upon just the prefix, you're going to have to do a search of the entire DOM (or at least, a search of an entire subtree if you know of some element that is always guaranteed to contain your target element). You can do this with something like:
function findChildWithIdLike(node, prefix) {
if (node && node.id && node.id.indexOf(prefix) == 0) {
//match found
return node;
}
//no match, check child nodes
for (var index = 0; index < node.childNodes.length; index++) {
var child = node.childNodes[index];
var childResult = findChildWithIdLike(child, prefix);
if (childResult) {
return childResult;
}
}
};
Here is an example: http://jsfiddle.net/xwqKh/
Be aware that dynamic element ids like the ones you are working with are typically used to guarantee uniqueness of element ids on a single page. Meaning that it is likely that there are multiple elements that share the same prefix. Probably you want to find them all.
If you want to find all of the elements that have a given prefix, instead of just the first one, you can use something like what is demonstrated here: http://jsfiddle.net/xwqKh/1/

I'm not entirely sure I know what you're asking about, but you can use string functions to create the actual ID that you're looking for.
var base = "common";
var num = 3;
var o = document.getElementById(base + num); // will find id="common3"
If you don't know the actual ID, then you can't look up the object with getElementById, you'd have to find it some other way (by class name, by tag type, by attribute, by parent, by child, etc...).
Now that you've finally given us some of the HTML, you could use this plain JS to find all form elements that have an ID that starts with "poll-":
// get a list of all form objects that have the right type of ID
function findPollForms() {
var list = getElementsByTagName("form");
var results = [];
for (var i = 0; i < list.length; i++) {
var id = list[i].id;
if (id && id.search(/^poll-/) != -1) {
results.push(list[i]);
}
}
return(results);
}
// return the ID of the first form object that has the right type of ID
function findFirstPollFormID() {
var list = getElementsByTagName("form");
var results = [];
for (var i = 0; i < list.length; i++) {
var id = list[i].id;
if (id && id.search(/^poll-/) != -1) {
return(id);
}
}
return(null);
}

You'll probably have to either give it a constant class and call getElementsByClassName, or maybe just use getElementsByTagName, and loop through your results, checking the name.
I'd suggest looking at your underlying problem and figure out a way where you can know the ID in advance.
Maybe if you posted a little more about why you're getting this, we could find a better alternative.

You use the id property to the get the id, then the substr method to remove the first part of it, then optionally parseInt to turn it into a number:
var id = theElement.id.substr(5);
or:
var id = parseInt(theElement.id.substr(5));

<form class="form-poll" id="poll-1225962377536" action="/cs/Satellite" target="_blank">
The ID always starts with 'post-' then the numbers are dynamic.
Please check your id names, "poll" and "post" are very different.
As already answered, you can use querySelector:
var selectors = '[id^="poll-"]';
element = document.querySelector(selectors).id;
but querySelector will not find "poll" if you keep querying for "post": '[id^="post-"]'

If you need last id, you can do that:
var id_list = document.querySelectorAll('[id^="image-"]')
var last_id = id_list.length
alert(last_id)