how to iterate on HTMLCollection? [duplicate]

问题

This question already has answers here:

Why does jQuery or a DOM method such as getElementById not find the element? (8 answers)

Is Chrome's JavaScript console lazy about evaluating arrays? (6 answers)

Use spread operator on NodeList in Typescript (1 answer)

Closed last year.

I have some elements in my HTML with class node-item, I access them in my component using:

let nodeItems = document.getElementsByClassName('node-item');

and when I log nodeItems it gives me a HTMLCollection[] with length 4.

I tried many ways but still can't iterate on nodeItems:

1- first try:

let bar = [].slice.call(nodeItems);
for (var g of bar){
    console.log(g); //gives me nothing
} 

2- second try:

for(let c of <any>nodeItems) {
    console.log(c); //gives me nothing
}

And I tried array iteration and object iteration but still undefined or error. also tried:

let nodeItems = document.querySelector(selectors);

But same problems.

回答1:

nodeItems is HTMLCollection, which is array-like object.

It is iterable in modern browsers. Iterators are supported with downlevelIteration compiler option enabled, in this case it will be:

const nodeItems = document.getElementsByClassName('node-item');

for (const c of nodeItems) {
  // ...
}

Iterables can be polyfilled in older browsers. core-js provides polyfills for DOM iterables.

Otherwise nodeItems can be converted to array and iterated as usual:

const nodeItems = Array.from(document.getElementsByClassName('node-item'));

for (const c of nodeItems) {
  // ...
}

回答2:

Just use Array.from(document.getElementsByClassName('node-item')) or the spread operator [...document.getElementsByClassName('node-item')] and use whatever you would use on an array.

Apart from that, you could also use a normal for loop

let nodeItems = document.getElementsByClassName('node-item');
for (let i = 0; i < nodeItems.length; i++) {
    // access current element with nodeItems[i]
}

回答3:

You can use spread operator on document.querySelectorAll to have an array.

Here is a snippet:

let nodeItems = [...(document.querySelectorAll('.class1'))];

for (var g of nodeItems) {
  console.log( g.innerHTML ); 
}

<div class='class1'>Text 1</div>
<div class='class1'>Text 2</div>
<div class='class1'>Text 3</div>

Doc: Spread

来源：https://stackoverflow.com/questions/49956141/how-to-iterate-on-htmlcollection