Using forEach on an array from getElementsByClassName results in “TypeError: undefined is not a function”
JavascriptForeachJavascript Problem Overview
In my JSFiddle, I’m simply trying to iterate over an array of elements. The array is non-empty, as the log statements prove. Yet the call to forEach gives me the (not so helpful) “Uncaught TypeError: undefined is not a function” error.
I must be doing something stupid; what am I doing wrong?
My code:
var arr = document.getElementsByClassName('myClass');
console.log(arr);
console.log(arr[0]);
arr.forEach(function(v, i, a) {
console.log(v);
});
.myClass {
background-color: #FF0000;
}
<div class="myClass">Hello</div>
Javascript Solutions
Solution 1 - Javascript
That's because document.getElementsByClassName returns a HTMLCollection, not an array.
Fortunately it's an "array-like" object (which explains why it's logged as if it was an object and why you can iterate with a standard for loop), so you can do this :
[].forEach.call(document.getElementsByClassName('myClass'), function(v,i,a) {
With ES6 (on modern browsers or with Babel), you may also use Array.from which builds arrays from array-like objects:
Array.from(document.getElementsByClassName('myClass')).forEach(v=>{
or spread the array-like object into an array:
[...document.getElementsByClassName('myClass'))].forEach(v=>{
Solution 2 - Javascript
Try this it should work :
<html>
<head>
<style type="text/css">
</style>
</head>
<body>
<div class="myClass">Hello</div>
<div class="myClass">Hello</div>
<script type="text/javascript">
var arr = document.getElementsByClassName('myClass');
console.log(arr);
console.log(arr[0]);
arr = [].slice.call(arr); //I have converted the HTML Collection an array
arr.forEach(function(v,i,a) {
console.log(v);
});
</script>
<style type="text/css">
.myClass {
background-color: #FF0000;
}
</style>
</body>
</html>
Solution 3 - Javascript
in the event that you want to access the ID of each element of a specific class you can do the following:
Array.from(document.getElementsByClassName('myClass')).forEach(function(element) {
console.log(element.id);
});