es5-shim: A JavaScript repository from javadoug

es5-shim.js and es5-shim.min.js monkey-patch a JavaScript context to contain all EcmaScript 5 methods that can be faithfully emulated with a legacy JavaScript engine.

es5-sham.js and es5-sham.min.js monkey-patch other ES5 methods as closely as possible. For these methods, as closely as possible to ES5 is not very close. Many of these shams are intended only to allow code to be written to ES5 without causing run-time errors in older engines. In many cases, this means that these shams cause many ES5 methods to silently fail. Decide carefully whether this is what you want.

Tests

The tests are written with the Jasmine BDD test framework. To run the tests, navigate to /tests/.

In order to run against the shim-code, the tests attempt to kill the current implementation of the missing methods. This happens in /tests/helpers/h-kill.js. So in order to run the tests against the build-in methods, invalidate that file somehow (comment-out, delete the file, delete the script-tag, etc.).

Shims

Complete tests

Array.prototype.every
Array.prototype.filter
Array.prototype.forEach
Array.prototype.indexOf
Array.prototype.lastIndexOf
Array.prototype.map
Array.prototype.some
Array.prototype.reduce
Array.prototype.reduceRight
Array.isArray
Date.now
Date.prototype.toJSON
Function.prototype.bind
- /!\ Caveat: the bound function's length is always 0.
- /!\ Caveat: the bound function has a prototype property.
- /!\ Caveat: bound functions do not try too hard to keep you from manipulating their arguments and caller properties.
- /!\ Caveat: bound functions don't have checks in call and apply to avoid executing as a constructor.
Object.keys
String.prototype.trim

Untested

Date.parse (for ISO parsing)
Date.prototype.toISOString

Shams

/?\ Object.create

For the case of simply "begetting" an object that inherits prototypically from another, this should work fine across legacy engines.

/!\ Object.create(null) will work only in browsers that support prototype assignment. This creates an object that does not have any properties inherited from Object.prototype. It will silently fail otherwise.

/!\ The second argument is passed to Object.defineProperties which will probably fail silently.
/?\ Object.getPrototypeOf

This will return "undefined" in some cases. It uses proto if it's available. Failing that, it uses constructor.prototype, which depends on the constructor property of the object's prototype having not been replaced. If your object was created like this, it won't work:
```
  function Foo() {
  }
  Foo.prototype = {};
```
Because the prototype reassignment destroys the constructor property.

This will work for all objects that were created using Object.create implemented with this library.
/!\ Object.getOwnPropertyNames

This method uses Object.keys, so it will not be accurate on legacy engines.
Object.isSealed

Returns "false" in all legacy engines for all objects, which is conveniently guaranteed to be accurate.
Object.isFrozen

Returns "false" in all legacy engines for all objects, which is conveniently guaranteed to be accurate.
Object.isExtensible

Works like a charm, by trying very hard to extend the object then redacting the extension.

Fail silently