Javascript: Object doesn't support method 'freeze'

Question

I am trying to create an enummeration in Javascript. The javascript code used is

var FeatureName = {
"FEATURE1": 1,
"FEATURE2": 2,
"FEATURE3": 3,
"FEATURE4": 4,
"FEATURE5": 5
}
Object.freeze(FeatureName);

When the method Object.freeze(FeatureName), is called it works fine for all the browsers except IE7 and IE8. Is there any alternative to this?

Answer 1

John Resig provides an alternative. I haven't tried it in the browsers you mention. Try it and let us know.

http://ejohn.org/blog/ecmascript-5-objects-and-properties/

Object.freeze = function( obj ) {
  var props = Object.getOwnPropertyNames( obj );

  for ( var i = 0; i < props.length; i++ ) {
    var desc = Object.getOwnPropertyDescriptor( obj, props[i] );

    if ( "value" in desc ) {
      desc.writable = false;
    }

     desc.configurable = false;
     Object.defineProperty( obj, props[i], desc );
  }

  return Object.preventExtensions( obj );
};

Answer 2

You can add include the es5-sham "monkey-patch" (only need to include es5-sham.min.js) on your page, but it's important to understand that this will simply prevent the error from appearing.

It's not a true polyfill though; from the project's README on Github:

Object.freeze

Silently fails on all legacy engines. This should be fine unless you are depending on the safety and security provisions of this method, which you cannot possibly obtain in legacy engines.

This library is also available from cdnjs if you want to use a CDN.

You can include it with code like this (note the tags limiting it to IE version 8 and older):

<!--[if lt IE 9]>
<script src="//cdnjs.cloudflare.com/ajax/libs/es5-shim/4.0.5/es5-sham.min.js" type="text/javascript"></script>
<![endif]-->