IE only javascript error with getElementsByTagName

Question

I have the following code which works in FF / Chrome ``` var stack = [Array.prototype.slice.call(document.getElementsByTagName("body")[0].childNodes)], nodes, node, parent, text, offset; while (stack.length) { nodes = stack.pop(); for (var i=0, n=nodes.length; i<n; ++i) { node = nodes[i]; switch (node.nodeType) { case Node.ELEMENT_NODE: if (node.nodeName.toUpperCase() !== "SCRIPT") { stack.push(Array.prototype.slice.call(node.childNodes)); } break; case Node.TEXT_NODE: text = node.nodeValue; offset = text.indexOf("[test="); if (offset >= 0 && text.substr(offset).match(/^($$test=(\d+)$$)/)) { parent = node.parentNode; var before = document.createTextNode(text.substr(0, offset)); link = document.createElement("a"), after = document.createTextNode(text.substr(offset + RegExp.$1.length)); link.appendChild(document.createTextNode(text.substr(offset, RegExp.$1.length))); link.setAttribute("href", "http://example.com/" + RegExp.$2); parent.insertBefore(after, node); parent.insertBefore(link,…

Accepted Answer

It's not legal to call `Array.prototype.slice` on a `NodeList` object as returned by the `childNodes` property (or various other DOM methods).

Normally it wouldn't be legal to call `Thing.prototype.method` on anything but an instance of `Thing`, however browsers have traditionally allowed — and the ECMAScript Third Edition standard requires — a special case for many `Array.prototype` methods so that they can be called on any native-JavaScript object which is sufficiently like an `Array`. This means, notably, that they can be used on the `arguments` object, which looks like an `Array` but actually isn't.

However, `NodeList` and the other collection objects in the DOM are not defined to be native JavaScript objects; they are allowed to be ‘host objects’, which are implemented completely by the browser and not the language. All bets are off for host objects...

Whether the slice function can be applied successfully to a host object is implementation-dependent.

So `Array.prototype.slice` may not work for NodeList, and in IE before version 8, indeed, it won't.

If you want to make a plain-Array copy of a NodeList, you'll have to do it the long but safe way:

```
Array.fromSequence= function(seq) {
    var arr= new Array(seq.length);
    for (var i= seq.length; i-->0;)
        if (i in seq)
            arr[i]= seq[i];
    return arr;
};

var stack = [Array.fromSequence(document.body.childNodes)];
```

Incidentally, you can make that linkifier a bit simpler by using `textnode.splitText`, and I'd be very wary about using the global `RegExp` properties, as if any unexpected regex work occurs in one of the intervening calls they'll be lost. Looking at the match object is usually better. See this question for another attack at basically the same problem.

IE only javascript error with getElementsByTagName

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