Add NodeList polyfills

At the guardian we realized yesterday, that there is currently no polyfill for NodeList.forEach(). According to MDN there is no support for the feature in the following browsers:

Browser	Version
Chrome	< 51
Firefox	<50
IE	*
Opera	<38
Safari	<10

The possible polyfill would be quite small:

if (window.NodeList && !NodeList.prototype.forEach) {
    NodeList.prototype.forEach = function (callback, argument) {
        argument = argument || window;
        for (var i = 0; i < this.length; i++) {
            callback.call(argument, this[i], i, this);
        }
    };
}

Do you think it’s worth adding this as a single polyfill, or would you rather like to polyfill all potential missing methods on NodeList, which are .entries(), forEach(), item(), keys(), values()?

I’m happy to work on a PR for this.

[Sora2455]

Just to summarise the thread so far:

1. NodeList is defined as iterable in the DOM Living Standard
2. Iterable is defined as having a foreach method in the Web IDL Candidate Recomendation
3. According to MDN, the current versions of Edge, Chrome, Firefox, Opera and Safari all support foreach on Nodelist (at the time of writing).

As this is such an easy thing to polyfill, I say yes, definitely add it.

[loilo]

For anyone subscribed to this: This feature is available in polyfill.io v3 which has been out for a couple days.

It’s not in the default feature set though, you have to include it manually:

https://polyfill.io/v3/polyfill.min.js?features=default,NodeList.prototype.forEach

@JakeChampion and others, looks like this issue can be closed now.