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
In order to run against the shim-code, the tests attempt to kill the current
implementation of the missing methods. This happens in
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
argumentsandcallerproperties. - /!\ Caveat: bound functions don't have checks in
callandapplyto 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.createimplemented 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
/!\ Object.getOwnPropertyDescriptor
The behavior of this shim does not conform to ES5. It should probably not be used at this time, until its behavior has been reviewed and been confirmed to be useful in legacy engines.
/!\ Object.defineProperty
This method will silently fail to set "writable", "enumerable", and "configurable" properties.
Providing a getter or setter with "get" or "set" on a descriptor will silently fail on engines that lack "defineGetter" and "defineSetter", which include all versions of IE up to version 8 so far.
IE 8 provides a version of this method but it only works on DOM objects. Thus, the shim will not get installed and attempts to set "value" properties will fail silently on non-DOM objects.
/!\ Object.defineProperties
This uses the Object.defineProperty shim
Object.seal
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.
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.
Object.preventExtensions
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.
