Advertisement
Advertisement


forEach is not a function error with JavaScript array


Question

I'm trying to make a simple loop:

const parent = this.el.parentElement
console.log(parent.children)
parent.children.forEach(child => {
  console.log(child)
})

But I get the following error:

VM384:53 Uncaught TypeError: parent.children.forEach is not a function

Even though parent.children logs:

enter image description here

What could be the problem?

Note: Here's a JSFiddle.

2016/03/13
1
152
3/13/2016 12:21:57 PM

Accepted Answer

First option: invoke forEach indirectly

The parent.children is an Array like object. Use the following solution:

const parent = this.el.parentElement;

Array.prototype.forEach.call(parent.children, child => {
  console.log(child)
});

The parent.children is NodeList type, which is an Array like object because:

  • It contains the length property, which indicates the number of nodes
  • Each node is a property value with numeric name, starting from 0: {0: NodeObject, 1: NodeObject, length: 2, ...}

See more details in this article.


Second option: use the iterable protocol

parent.children is an HTMLCollection: which implements the iterable protocol. In an ES2015 environment, you can use the HTMLCollection with any construction that accepts iterables.

Use HTMLCollection with the spread operatator:

const parent = this.el.parentElement;

[...parent.children].forEach(child => {
  console.log(child);
});

Or with the for..of cycle (which is my preferred option):

const parent = this.el.parentElement;

for (const child of parent.children) {
  console.log(child);
}
2020/02/20
132
2/20/2020 11:35:10 AM


parent.children will return a node list list, technically a html Collection. That is an array like object, but not an array, so you cannot call array functions over it directly. At this context you can use Array.from() to convert that into a real array,

Array.from(parent.children).forEach(child => {
  console.log(child)
})

A more naive version, at least you're sure that it'll work on all devices, without conversion and ES6 :

const children = parent.children;
for (var i = 0; i < children.length; i++){
    console.log(children[i]);
}

https://jsfiddle.net/swb12kqn/5/

2020/03/27

parent.children is a HTMLCollection which is array-like object. First, you have to convert it to a real Array to use Array.prototype methods.

const parent = this.el.parentElement
console.log(parent.children)
[].slice.call(parent.children).forEach(child => {
  console.log(child)
})
2016/03/13

There is no need for the forEach, you can iterate using only the from's second parameter, like so:

let nodeList = [{0: [{'a':1,'b':2},{'c':3}]},{1:[]}]
Array.from(nodeList, child => {
  console.log(child)
});

2017/08/25

That's because parent.children is a NodeList, and it doesn't support the .forEach method (as NodeList is an array like structure but not an array), so try to call it by first converting it to array using

var children = [].slice.call(parent.children);
children.forEach(yourFunc);
2016/03/13