Question

I’m trying to get:

document.createElement('div')  //=> true {tagName: 'foobar something'}  //=> false 

In my own scripts, I used to just use this since I never needed tagName as a property:

if (!object.tagName) throw ...; 

So for the second object, I came up with the following as a quick solution — which mostly works. 😉

The problem is, it depends on browsers enforcing read-only properties, which not all do.

function isDOM(obj) {   var tag = obj.tagName;   try {     obj.tagName = '';  // Read-only for DOM, should throw exception     obj.tagName = tag; // Restore for normal objects     return false;   } catch (e) {     return true;   } } 

Is there a good substitute?

Answer 1

This might be of interest:

function isElement(obj) {   try {     //Using W3 DOM2 (works for FF, Opera and Chrome)     return obj instanceof HTMLElement;   }   catch(e){     //Browsers not supporting W3 DOM2 don't have HTMLElement and     //an exception is thrown and we end up here. Testing some     //properties that all elements have (works on IE7)     return (typeof obj==='object') &&       (obj.nodeType===1) && (typeof obj.style === 'object') &&       (typeof obj.ownerDocument ==='object');   } } 

It’s part of the DOM, Level2.

Update 2: This is how I implemented it in my own library: (the previous code didn’t work in Chrome, because Node and HTMLElement are functions instead of the expected object. This code is tested in FF3, IE7, Chrome 1 and Opera 9).

//Returns true if it is a DOM node function isNode(o){   return (     typeof Node === 'object' ? o instanceof Node :      o && typeof o === 'object' && typeof o.nodeType === 'number' && typeof o.nodeName==='string'   ); }  //Returns true if it is a DOM element     function isElement(o){   return (     typeof HTMLElement === 'object' ? o instanceof HTMLElement : //DOM2     o && typeof o === 'object' && o !== null && o.nodeType === 1 && typeof o.nodeName==='string' ); }