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easejs/lib/util.js

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/**
* Contains utilities functions shared by modules
*
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* Copyright (C) 2010, 2011, 2012, 2013 Mike Gerwitz
*
* This file is part of GNU ease.js.
*
* ease.js is free software: you can redistribute it and/or modify
* it under the terms of the GNU 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
var propParseKeywords = require( __dirname + '/prop_parser' ).parseKeywords;
/**
* Whether we can actually define properties, or we need to fall back
*
* This check actually attempts to set a property and fails if there's an error.
* This is needed because IE8 has a broken implementation, yet still defines
* Object.defineProperty for use with DOM elements. Just another day in the life
* of a web developer.
*
* This test is only performed once, when the module is first loaded. Don't
* expect a performance hit from it.
*
* @type {boolean}
*/
var can_define_prop = ( function()
{
if ( typeof Object.defineProperty === 'function' )
{
try
{
// perform test, primarily for IE8
Object.defineProperty( {}, 'x', {} );
return true;
}
catch ( e ) {}
}
return false;
} )();
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/**
* Freezes an object if freezing is supported
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*
* @param {Object} obj object to freeze
*
* @return {Object} object passed to function
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*/
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exports.freeze = ( typeof Object.freeze === 'function' )
? Object.freeze
: function( obj )
{
return;
}
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;
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/**
* Gets/sets whether the system needs to fall back to defining properties in a
* normal manner when use of Object.defineProperty() is requested
*
* This will be set by default if the JS engine does not support the
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* Object.defineProperty method from ECMAScript 5.
*
* @param {boolean=} val value, if used as setter
*
* @return {boolean|Object} current value if getter, self if setter
*/
exports.definePropertyFallback = function( val )
{
if ( val === undefined )
{
return !can_define_prop;
}
can_define_prop = !val;
exports.defineSecureProp = getDefineSecureProp();
return exports;
};
/**
* Attempts to define a non-enumerable, non-writable and non-configurable
* property on the given object
*
* If the operation is unsupported, a normal property will be set.
*
* @param {Object} obj object to set property on
* @param {string} prop name of property to set
* @param {*} value value to set
*
* @return {undefined}
*/
exports.defineSecureProp = getDefineSecureProp();
/**
* Clones an object
*
* @param {*} data object to clone
* @param {boolean=} deep perform deep clone (defaults to shallow)
*
* @return {*} cloned object
*
* Closure Compiler ignores typeof checks and is thusly confused:
* @suppress {checkTypes}
*/
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exports.clone = function clone( data, deep )
{
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deep = !!deep;
if ( data instanceof Array )
{
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if ( !deep )
{
// return a copy of the array
return data.slice( 0 );
}
// if we're performing a deep clone, we have to loop through each of the
// elements of the array and clone them
var ret = [];
for ( var i = 0, len = data.length; i < len; i++ )
{
// clone this element
ret.push( clone( data[ i ], deep ) );
}
return ret;
}
else if ( typeof data === 'function' )
{
// It is pointless to clone a function. Even if we did clone those that
// support toSource(), they'd still do the same damn thing.
return data;
}
// explicitly testing with instanceof will ensure we're actually testing an
// object, not something that may be misinterpreted as one (e.g. null)
else if ( data instanceof Object )
{
var newobj = {},
hasOwn = Object.prototype.hasOwnProperty;
// copy data to the new object
for ( var prop in data )
{
if ( hasOwn.call( data, prop ) )
{
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newobj[ prop ] = ( deep )
? clone( data[ prop ] )
: data[ prop ]
;
}
}
return newobj;
}
// primitive type; cloning unnecessary
return data;
};
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/**
* Copies properties from one object to another
*
* This method is designed to support very basic object extensions. The
* destination argument is first to allow extending an object without using the
* full-blown class system.
*
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* If a deep copy is not performed, all values will be copied by reference.
*
* @param {Object} dest destination object
* @param {Object} src source object
* @param {boolean} deep perform deep copy (slower)
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*
* @return {Object} dest
*/
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exports.copyTo = function( dest, src, deep )
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{
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deep = !!deep;
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var get, set, data;
// sanity check
if ( !( dest instanceof Object ) || !( src instanceof Object ) )
{
throw TypeError(
"Must provide both source and destination objects"
);
}
// slower; supports getters/setters
if ( can_define_prop )
{
for ( var prop in src )
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{
data = Object.getOwnPropertyDescriptor( src, prop );
if ( data.get || data.set )
{
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// Define the property the slower way (only needed for
// getters/setters). We don't have to worry about cloning in
// this case, since getters/setters are methods.
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Object.defineProperty( dest, prop, data );
}
else
{
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// normal copy; cloned if deep, otherwise by reference
dest[ prop ] = ( deep )
? exports.clone( src[ prop ], true )
: src[ prop ]
;
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}
}
}
// quick (keep if statement out of the loop)
else
{
for ( var prop in src )
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{
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// normal copy; cloned if deep, otherwise by reference
dest[ prop ] = ( deep )
? exports.clone( src[ prop ], true )
: src[ prop ]
;
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}
}
// return dest for convenience (and to feel useful about ourselves)
return dest;
};
/**
* Parses object properties to determine how they should be interpreted in an
* Object Oriented manner
*
* @param {!Object} data properties with names as the key
*
* @param {!{each,property,method,getset,keywordParser}} options
* parser options and callbacks
*
* @return undefined
*/
exports.propParse = function( data, options )
{
// todo: profile; function calls are more expensive than if statements, so
// it's probably a better idea not to use fvoid
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var fvoid = function() {},
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callbackEach = options.each || undefined,
callbackProp = options.property || fvoid,
callbackMethod = options.method || fvoid,
callbackGetSet = options.getset || fvoid,
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keywordParser = options.keywordParser || propParseKeywords,
hasOwn = Object.prototype.hasOwnProperty,
parse_data = {},
name = '',
keywords = {},
value = null,
getter = false,
setter = false;
// for each of the given properties, determine what type of property we're
// dealing with (in the classic OO sense)
for ( var prop in data )
{
// ignore properties of instance prototypes
if ( !( hasOwn.call( data, prop ) ) )
{
continue;
}
// retrieve getters/setters, if supported
if ( can_define_prop )
{
var prop_desc = Object.getOwnPropertyDescriptor( data, prop );
getter = prop_desc.get;
setter = prop_desc.set;
}
// do not attempt to retrieve the value if a getter is defined (as that
// would then call the getter)
value = ( typeof getter === 'function' )
? undefined
: data[ prop ];
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parse_data = keywordParser( prop ) || {};
name = parse_data.name || prop;
keywords = parse_data.keywords || {};
if ( options.assumeAbstract || keywords[ 'abstract' ] )
{
// may not be set if assumeAbstract is given
keywords[ 'abstract' ] = true;
if ( !( value instanceof Array ) )
{
throw TypeError(
"Missing parameter list for abstract method: " + name
);
}
verifyAbstractNames( name, value );
value = exports.createAbstractMethod.apply( this, value );
}
// if an 'each' callback was provided, pass the data before parsing it
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if ( callbackEach )
{
callbackEach.call( callbackEach, name, value, keywords );
}
// getter/setter
if ( getter || setter )
{
callbackGetSet.call( callbackGetSet,
name, getter, setter, keywords
);
}
// method
Added `proxy' keyword support The concept of proxy methods will become an important, core concept in ease.js that will provide strong benefits for creating decorators and proxies, removing boilerplate code and providing useful metadata to the system. Consider the following example: Class( 'Foo', { // ... 'public performOperation': function( bar ) { this._doSomethingWith( bar ); return this; }, } ); Class( 'FooDecorator', { 'private _foo': null, // ... 'public performOperation': function( bar ) { return this._foo.performOperation( bar ); }, } ); In the above example, `FooDecorator` is a decorator for `Foo`. Assume that the `getValueOf()` method is undecorated and simply needs to be proxied to its component --- an instance of `Foo`. (It is not uncommon that a decorator, proxy, or related class will alter certain functionality while leaving much of it unchanged.) In order to do so, we can use this generic, boilerplate code return this.obj.func.apply( this.obj, arguments ); which would need to be repeated again and again for *each method that needs to be proxied*. We also have another problem --- `Foo.getValueOf()` returns *itself*, which `FooDecorator` *also* returns. This breaks encapsulation, so we instead need to return ourself: 'public performOperation': function( bar ) { this._foo.performOperation( bar ); return this; }, Our boilerplate code then becomes: var ret = this.obj.func.apply( this.obj, arguments ); return ( ret === this.obj ) ? this : ret; Alternatively, we could use the `proxy' keyword: Class( 'FooDecorator2', { 'private _foo': null, // ... 'public proxy performOperation': '_foo', } ); `FooDecorator2.getValueOf()` and `FooDecorator.getValueOf()` both perform the exact same task --- proxy the entire call to another object and return its result, unless the result is the component, in which case the decorator itself is returned. Proxies, as of this commit, accomplish the following: - All arguments are forwarded to the destination - The return value is forwarded to the caller - If the destination returns a reference to itself, it will be replaced with a reference to the caller's context (`this`). - If the call is expected to fail, either because the destination is not an object or because the requested method is not a function, a useful error will be immediately thrown (rather than the potentially cryptic one that would otherwise result, requiring analysis of the stack trace). N.B. As of this commit, static proxies do not yet function properly.
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else if ( ( typeof value === 'function' ) || ( keywords[ 'proxy' ] ) )
{
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callbackMethod.call(
callbackMethod,
name,
value,
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exports.isAbstractMethod( value ),
keywords
);
}
// simple property
else
{
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callbackProp.call( callbackProp, name, value, keywords );
}
}
};
/**
* Only permit valid names for parameter list
*
* In the future, we may add additional functionality, so it's important to
* restrict this as much as possible for the time being.
*
* @param {string} name name of abstract member (for error)
* @param {Object} params parameter list to check
*
* @return {undefined}
*/
function verifyAbstractNames( name, params )
{
var i = params.length;
while ( i-- )
{
if ( params[ i ].match( /^[a-z_][a-z0-9_]*$/i ) === null )
{
throw SyntaxError(
"Member " + name + " contains invalid parameter '" +
params[ i ] + "'"
);
}
}
}
/**
* Creates an abstract method
*
* Abstract methods must be implemented by a subclass and cannot be called
* directly. If a class contains a single abstract method, the class itself is
* considered to be abstract and cannot be instantiated. It may only be
* extended.
*
* @param {...string} def function definition that concrete
* implementations must follow
*
* @return {function()}
*/
exports.createAbstractMethod = function( def )
{
var definition = Array.prototype.slice.call( arguments );
var method = function()
{
throw new Error( "Cannot call abstract method" );
};
exports.defineSecureProp( method, 'abstractFlag', true );
exports.defineSecureProp( method, 'definition', definition );
exports.defineSecureProp( method, '__length', arguments.length );
return method;
};
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/**
* Determines if the given function is an abstract method
*
* @param {function()} func function to inspect
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*
* @return {boolean} true if function is an abstract method, otherwise false
*
* @suppress {checkTypes}
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*/
exports.isAbstractMethod = function( func )
{
return ( ( typeof func === 'function') && ( func.abstractFlag === true ) )
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? true
: false
;
};
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/**
* Shrinks an array, removing undefined elements
*
* Pushes all items onto a new array, removing undefined elements. This ensures
* that the length of the array represents correctly the number of elements in
* the array.
*
* @param {Array} items array to shrink
*
* @return {Array} shrunken array
*/
exports.arrayShrink = function( items )
{
// copy the methods into a new array by pushing them onto it, to ensure
// the length property of the array will work properly
var arr_new = [];
for ( var i = 0, len = items.length; i < len; i++ )
{
var item = items[ i ];
if ( item === undefined )
{
continue;
}
arr_new.push( item );
}
return arr_new;
};
/**
* Uses Object.getOwnPropertyDescriptor if available, otherwise provides our own
* implementation to fall back on
*/
exports.getOwnPropertyDescriptor =
( can_define_prop && Object.getOwnPropertyDescriptor ) ||
/**
* 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|undefined} descriptor for requested property, if found
*/
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 ],
};
};
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/**
* Returns prototype of object, or undefined if unsupported
*/
exports.getPrototypeOf = Object.getPrototypeOf || function()
{
return undefined;
};
/**
* 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().
*
* This method has the option to ignore the base prototype. This is useful to,
* for example, not catch properties like Object.prototype.toString() when
* searching for 'toString' on an object.
*
* @param {Object} obj object to check property on
* @param {string} prop property to retrieve descriptor for
* @param {boolean} nobase whether to ignore the base prototype
*
* @return {Object} descriptor for requested property or undefined if not found
*/
exports.getPropertyDescriptor = function( obj, prop, nobase )
{
// false by default
nobase = !!nobase;
// note that this uses util's function, not Object's
var desc = exports.getOwnPropertyDescriptor( obj, prop ),
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next = exports.getPrototypeOf( obj );
// if we didn't find a descriptor and a prototype is available, recurse down
// the prototype chain, ensuring that the next prototype has a prototype if
// the base is to be excluded
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if ( !desc && next && ( !nobase || exports.getPrototypeOf( next ) ) )
{
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return exports.getPropertyDescriptor( next, prop, nobase );
}
// 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
*/
exports.defineSecureProp( exports.getPropertyDescriptor, 'canTraverse',
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( Object.getPrototypeOf ) ? true : false
);
/**
* Appropriately returns defineSecureProp implementation to avoid check on each
* invocation
*
* @return {function( Object, string, * )}
*/
function getDefineSecureProp()
{
// falls back to simply defining a normal property
var fallback = function( obj, prop, value )
{
obj[ prop ] = value;
};
if ( !can_define_prop )
{
return fallback;
}
else
{
// uses ECMAScript 5's Object.defineProperty() method
return function( obj, prop, value )
{
try
{
Object.defineProperty( obj, prop,
{
value: value,
enumerable: false,
writable: false,
configurable: false,
});
}
catch ( e )
{
// let's not have this happen again, as repeatedly throwing
// exceptions will do nothing but slow down the system
exports.definePropertyFallback( true );
// if there's an error (ehem, IE8), fall back
fallback( obj, prop, value );
}
};
}
}