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`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 <root-folder>/tests/.
In order to run against the shim-code, the tests attempt to kill the current
implementation of the missing methods. This happens in <root-folder>/tests/helpers/h-kill.js.
So in order to run the tests against the built-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
* /!\ 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.
https://github.com/kriskowal/es5-shim/issues#issue/5
* /!\ 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.
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