Working around IE8's broken Object.definePrope

问题:

Consider the following code, using ECMAScript5's Object.defineProperty feature:

var sayHi = function(){ alert('hi'); };
var defineProperty = (typeof Object.defineProperty == 'function');
if (defineProperty) Object.defineProperty(Array.prototype,'sayHi',{value:sayHi});
else Array.prototype.sayHi = sayHi;
var a = [];
a.sayHi();

This works for Chrome and Firefox 4 (where defineProperty exists), and it works for Firefox 3.6 (where defineProperty does not exist). IE8, however, only partially supports defineProperty. As a result, it attempts to run the Object.defineProperty method, but then fails (with no error shown in the browser) and ceases to run all other JavaScript code on the page.

Is there a better way to detect and avoid IE8's broken implementation than:

if (defineProperty){
  try{ Object.defineProperty(Array.prototype,'sayHi',{value:sayHi}); }catch(e){};
}
if (!Array.prototype.sayHi) Array.prototype.sayHi = sayHi;

For the curious, I'm using this in my ArraySetMath library to define non-enumerable array methods in those browsers that support this, with a fallback to enumerable methods for older browsers.

回答1:

I don't think there's a better way than a direct feature test with try/catch. This is actually exactly what IE team itself recommends in this recent post on transitioning to ES5 API.

You can shorten the test to just something like Object.defineProperty({}, 'x', {}) (instead of using Array.prototype) but that's a minor quibble; your example tests exact functionality (and so has less chance of false positives).

回答2:

I'm using Browserify with the package pluralize from npm which uses Object.defineProperty and I dropped this in.

https://github.com/inexorabletash/polyfill/blob/master/es5.js

回答3:

I stumbled on this before. IMHO using a try…catch statement is too drastic.
Something more efficient would be to use conditional compilation:

/*@cc_on@if(@_jscript_version>5.8)if(document.documentMode>8)@*/
Object.defineProperty && Object.defineProperty(Array.prototype,'sayHi',{value:sayHi});
/*@end@*/ 

回答4:

I had the same kind issue (i.e. the Object.defineProperty in IE 8 being DOM only and not a full implementation as the other browsers), but it was for a polyfill..

Anyhoo, I ended using a 'feature' check to see if I was using IE, its not perfect, but it works on all the tests I could do:

if (Object.defineProperty && !document.all && document.addEventListener) {
    Object.defineProperty(Array.prototype,'sayHi',{value:sayHi});
} else {
    Array.prototype.sayHi = sayHi;
}

as IE <= 8 has no document.addEventListener, and document.all is a proprietary Microsoft extension to the W3C standard. These two checks are equivalent to checking if IE is version 8 or below.

回答5:

Array.prototype.sayHi = function(){ alert('hi'); };

try {
  Object.defineProperty(Array.prototype, 'sayHi', {
    value: Array.prototype.sayHi
  });
}
catch(e){};