JQuery to check for duplicate ids in a DOM
JqueryDomJquery Problem Overview
I'm writing applications with ASP.NET MVC. In contrast to traditional ASP.NET you're a lot more responsible for creating all the ids in your generated page. ASP.NET would give you nasty, but unique ids.
I'd like to add a quick little jQuery script to check my document for duplicate ids. They may be ids for DIVS, images, checkboxes, buttons etc.
<div id="pnlMain"> My main panel </div>
<div id="pnlMain"> Oops we accidentally used the same ID </div>
I'm looking for a set and forget type utility that'll just warn me when I do something careless.
Yes i'd be using this only during testing, and alternatives (such as firebug plugins) are welcome too.
Jquery Solutions
Solution 1 - Jquery
The following will log a warning to the console:
// Warning Duplicate IDs
$('[id]').each(function(){
var ids = $('[id="'+this.id+'"]');
if(ids.length>1 && ids[0]==this)
console.warn('Multiple IDs #'+this.id);
});
Solution 2 - Jquery
This version is somewhat faster, and you can copy it to a bookmark button to make it a bookmarklet.
javascript:(function () {
var ids = {};
var found = false;
$('[id]').each(function() {
if (this.id && ids[this.id]) {
found = true;
console.warn('Duplicate ID #'+this.id);
}
ids[this.id] = 1;
});
if (!found) console.log('No duplicate IDs found');
})();
Solution 3 - Jquery
I have a big page, so that script runs too slow to finish (multiple "continue script" messages). This works fine.
(function () {
var elms = document.getElementsByTagName("*"), i, len, ids = {}, id;
for (i = 0, len = elms.length; i < len; i += 1) {
id = elms[i].id || null;
if (id) {
ids[id] = ids.hasOwnProperty(id) ? ids[id] +=1 : 0;
}
}
for (id in ids) {
if (ids.hasOwnProperty(id)) {
if (ids[id]) {
console.warn("Multiple IDs #" + id);
}
}
}
}());
Solution 4 - Jquery
You should try HTML Validator (Firefox extension). It'll definitely tell you the page has duplicate ids and much more.
Solution 5 - Jquery
Why don't you just validate your html?
Double ID's are not allowed, and normally you will get a parse-error.
Solution 6 - Jquery
The top jQuery answer, rewritten in ES6:
[...document.querySelectorAll('[id]')].forEach(el => {
const dups = document.querySelectorAll(`[id="${el.id}"]`);
if (dups[1] === el) {
console.error(`Duplicate IDs #${el.id}`, ...dups);
}
});
Solution 7 - Jquery
Yet another way of locating duplicates but this will add a class of error so it will have red text:
// waits for document load then highlights any duplicate element id's
$(function(){ highlight_duplicates();});
function highlight_duplicates() {
// add errors when duplicate element id's exist
$('[id]').each(function(){ // iterate all id's on the page
var elements_with_specified_id = $('[id='+this.id+']');
if(elements_with_specified_id.length>1){
elements_with_specified_id.addClass('error');
}
});
// update flash area when warning or errors are present
var number_of_errors = $('.error').length;
if(number_of_errors > 0)
$('#notice').append('<p class="error">The '+number_of_errors+
' items below in Red have identical ids. Please remove one of the items from its associated report!</p>');
}
Solution 8 - Jquery
This might do the trick It will alert all the ids of elements with duplicates.
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<html>
<head>
<script type="text/javascript" src="jquery-1.3.1.min.js"></script>
<script type="text/javascript">
function findDupes()
{
var all = $("*");
for(var i = 0; i < all.length; i++)
{
if (all[i].id.length > 0 && $("[id='" + all[i].id + "']").length > 1) alert(all[i].id);
}
}
</script>
</head>
<body onload="findDupes()">
<div id="s"></div>
<div id="f"></div>
<div id="g"></div>
<div id="h"></div>
<div id="d"></div>
<div id="j"></div>
<div id="k"></div>
<div id="l"></div>
<div id="d"></div>
<div id="e"></div>
</body>
</html>
Solution 9 - Jquery
I like this because it spits out the actual elements to the console. It makes it easier to investigate what's going on.
function CheckForDuplicateIds() {
var ids = {};
var duplicates = [];
$("[id]").each(function() {
var thisId = $(this).attr("id");
if (ids[thisId] == null) {
ids[thisId] = true;
} else {
if (ids[thisId] == true) {
duplicates.push(thisId);
ids[thisId] = false;
}
}
});
if (duplicates.length > 0) {
console.log("=======================================================");
console.log("The following " + duplicates.length + " ids are used by multiple DOM elements:");
console.log("=======================================================");
$(duplicates).each(function() {
console.warn("Elements with an id of " + this + ":");
$("[id='" + this + "']").each(function() {
console.log(this);
});
console.log("");
});
} else {
console.log("No duplicate ids were found.");
}
return "Duplicate ID check complete.";
}
Solution 10 - Jquery
You can use this solution which will print out in console a list of duplicate ids if any is present.
You can run the code directly in console (copy/paste) after you DOM is loaded and does not require additional dependence like jQuery.
You could use it to quickly found out possible errors in your HTML markup.
(function (document) {
var elms = document.body.querySelectorAll('*[id]'),
ids = [];
for (var i = 0, len = elms.length; i < len; i++) {
if (ids.indexOf(elms[i].id) === -1) {
ids.push(elms[i].id);
} else {
console.log('Multiple IDs #' + elms[i].id);
}
}
})(document);
An example:
https://jsbin.com/cigusegube/edit?html,console,output
(here code is added before closing the body tag)
Solution 11 - Jquery
I've created a function where you can inspect a specifically element searching for duplicated ids within or the entire page:
function duplicatedIDs(container) {
var $container = container ? $(container) : $('body'),
elements = {},
duplicatedIDs = 0;
totalIDs = 0;
$container.find('[ID]').each(function(){
var element = this;
if(elements[element.id]){
elements[element.id].push(element);
} else {
elements[element.id] = [element];
}
totalIDs += 1;
});
for( var k in elements ){
if(elements[k].length > 1){
console.warn('######################################')
console.warn(' ' + k )
console.warn('######################################')
console.log(elements[k]);
console.log('---------------------------------------');
duplicatedIDs += elements[k].length
}
}
console.info('totalIDs', totalIDs);
console.error('duplicatedIDs', duplicatedIDs);
}
duplicatedIDs('#element'); //find duplicated ids under that element
duplicatedIDs(); // entire page
Solution 12 - Jquery
We can directly paste the below script into browser console to get duplicate IDs
[...document.querySelectorAll('[id]')].filter(el => [...document.querySelectorAll('[id]')].map(el => el.id).filter(id => id === el.id).length > 1);
Reference: https://www.abeautifulsite.net/getting-duplicate-ids-in-an-html-document