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Added util.get{Own,}PropertyDescriptor

closure/master
Mike Gerwitz 2011-06-11 21:47:57 -04:00
parent d6873d1cc9
commit 75059ad030
2 changed files with 216 additions and 0 deletions

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@ -419,6 +419,85 @@ exports.arrayShrink = function( items )
}; };
/**
* Uses Object.getOwnPropertyDescriptor if available, otherwise provides our own
* implementation to fall back on
*
* If the environment does not support retrieving property descriptors (ES5),
* then the following will be true:
* - get/set will always be undefined
* - writable, enumerable and configurable will always be true
* - value will be the value of the requested property on the given object
*
* @param {Object} obj object to check property on
* @param {string} prop property to retrieve descriptor for
*
* @return {Object} descriptor for requested property or undefined if not found
*/
exports.getOwnPropertyDescriptor = Object.getOwnPropertyDescriptor
|| function( obj, prop )
{
if ( !Object.prototype.hasOwnProperty.call( obj, prop ) )
{
return undefined;
}
// fallback response
return {
get: undefined,
set: undefined,
writable: true,
enumerable: true,
configurable: true,
value: obj[ prop ],
};
};
/**
* Travels down the prototype chain of the given object in search of the
* requested property and returns its descriptor
*
* This operates as Object.getOwnPropertyDescriptor(), except that it traverses
* the prototype chain. For environments that do not support __proto__, it will
* not traverse the prototype chain and essentially serve as an alias for
* getOwnPropertyDescriptor().
*
* @param {Object} obj object to check property on
* @param {string} prop property to retrieve descriptor for
*
* @return {Object} descriptor for requested property or undefined if not found
*/
exports.getPropertyDescriptor = function( obj, prop )
{
// note that this uses util's function, not Object's
var desc = exports.getOwnPropertyDescriptor( obj, prop );
// if we didn't find a descriptor and a prototype is available, recurse down
// the prototype chain
if ( !desc && obj.__proto__ )
{
return exports.getPropertyDescriptor( obj.__proto__, prop );
}
// return the descriptor or undefined if no prototype is available
return desc;
};
/**
* Indicates whether or not the getPropertyDescriptor method is capable of
* traversing the prototype chain
*
* @type {boolean}
*/
exports.defineSecureProp( exports.getPropertyDescriptor, 'canTraverse',
( {}.__proto__ ) ? true : false
);
/** /**
* Appropriately returns defineSecureProp implementation to avoid check on each * Appropriately returns defineSecureProp implementation to avoid check on each
* invocation * invocation

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@ -0,0 +1,137 @@
/**
* Tests util.getPropertyDescriptor
*
* Copyright (C) 2010 Mike Gerwitz
*
* This file is part of ease.js.
*
* ease.js is free software: you can redistribute it and/or modify it under the
* terms of the GNU Lesser General Public License as published by the Free
* Software Foundation, either version 3 of the License, or (at your option)
* any later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
* for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* @author Mike Gerwitz
* @package test
*/
var common = require( './common' ),
assert = require( 'assert' ),
util = common.require( 'util' ),
get_set = !( util.definePropertyFallback() )
;
/**
* If Object.getOwnPropertyDescriptor is provided by our environment, it should
* be used by util
*/
( function testUtilGetOwnPropertyDescriptorIsObjectsIfAvailable()
{
if ( Object.getOwnPropertyDescriptor )
{
assert.strictEqual(
util.getOwnPropertyDescriptor,
Object.getOwnPropertyDescriptor,
"Util should use Object.getOwnPropertyDescriptor if available"
);
}
} )();
/**
* The function should provide a boolean value indicating whether it can
* traverse the prototype chain
*/
( function testIndicatesWhetherTraversalIsPossible()
{
var traversable = ( {}.__proto__ ) ? true : false;
assert.equal( util.getPropertyDescriptor.canTraverse, traversable,
"Indicates whether traversal is possible"
);
} )();
/**
* We don't want tricksters to get funky with our system
*/
( function testTraversablePropertyIsNonWritable()
{
var getDesc;
if ( get_set )
{
assert.equal(
Object.getOwnPropertyDescriptor(
util.getPropertyDescriptor, 'canTraverse'
).writable,
false,
"Should not be able to alter canTravese value"
);
}
} )();
/**
* The return value should mimic Object.getOwnPropertyDescriptor() if we're not
* having to traverse the prototype chain
*/
( function testActsExactlyAsGetOwnPropertyDescriptorInEs5SystemsOnSameObject()
{
var obj = { foo: 'bar' },
desc1 = util.getOwnPropertyDescriptor( obj, 'foo' ),
desc2 = util.getPropertyDescriptor( obj, 'foo' )
;
assert.deepEqual( desc1, desc2,
"When operating one level deep, should return same as " +
"Object.getOwnPropertyDescriptor"
);
} )();
/**
* If we *do* have to start traversing the prototype chain (which
* Object.getOwnPropertyDescriptor() cannot do), then it should be as if we
* called Object.getOwnPropertyDescriptor() on the object in the prototype chain
* containing the requested property.
*/
( function testTraversesThePrototypeChain()
{
// if we cannot traverse the prototype chain, this test is pointless
if ( !util.getPropertyDescriptor.canTraverse )
{
return;
}
var proto = { foo: 'bar' },
obj = function() {}
;
obj.prototype = proto;
// to give ourselves the prototype chain (we don't want to set __proto__
// because this test will also be run on pre-ES5 engines)
var inst = new obj(),
// get the actual descriptor
expected = util.getOwnPropertyDescriptor( proto, 'foo' ),
// attempt to gather the descriptor from the prototype chain
given = util.getPropertyDescriptor( inst, 'foo' )
;
assert.deepEqual( given, expected,
"Properly traverses the prototype chain to retrieve the descriptor"
);
} )();