一些JavaScript 1.6~1.8上的高级技巧～

在jslibs的项目wiki上看到这些技巧，都是一些在mozilla spidermonkey javascript上的高级戏法。在JScript上不能用的哈～。这里转过来，很多技巧挺有趣的。
原文引用在：
http://code.google.com/p/jslibs/wiki/JavascriptTips

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1.   destructuring assignments

^{JavaScript 1.7}

var { a : x } = { a : 7 };
Print ( x ); // prints: 7

2.   Generator Expressions

^{JavaScript 1.7}

[ y for ( y in [ 5 , 6 , 7 , 8 , 9 ] ) ] // is [0,1,2,3,4]

and

[ y for each ( y in [ 5 , 6 , 7 , 8 , 9 ] ) ] // is [5,6,7,8,9]

Because in for extracts index names, and for each extracts the values.

3.   Advanced use of iterators

^{JavaScript 1.8}

Number . prototype . __iterator__ = function () {

  for ( let i = 0 ; i < this ; i ++ )
  yield i ;
};

for ( let i in 5 )
  print ( i );

prints:

1
2
3
4
5

This make Number object to act as a generator.

4.   Expression Closures

^{JavaScript 1.8}

function ( x ) x * x ;

Note that braces { ... } and return are implicit

5.   Basic debugging

^{JavaScript 1.6}

LoadModule ( 'jsstd' );

function ThrowAnError () {

  ( function (){

    throw new Error ( "Whoops!" );
  })();
}

try {

    ThrowAnError ()
} catch ( e ) {

    Print ( e . stack );
}

prints:

Error ( "Whoops!" ) @ : 0
() @test . js : 7
ThrowAnError () @test . js : 5
@test . js : 14

6.   Multiple-value returns

^{JavaScript 1.7}

function f () {

  return [ 1 , 2 ];
}

var [ a , b ] = f ();

Print ( a + ' ' + b ); // prints: 1 2

7.   Operator [ ] and strings ( like charAt() )

^{JavaScript 1.6}

var str = 'foobar' ;
Print ( str [ 4 ] );

prints:

a

8.   indexOf() and lastIndexOf() Works on Array

^{JavaScript 1.6}

var obj = {};
var arr = [ 'foo' , 567 , obj , 12 . 34 ];
Print ( arr . indexOf ( obj ) ); // prints: 2

9.   Using Array functions on a non-Array object

^{JavaScript 1.7}

var obj = {};
Array . push ( obj , 'foo' );
Array . push ( obj , 123 );
Array . push ( obj , 5 . 55 );
Print ( obj . toSource () ); // prints: ({0:"foo", length:3, 1:123, 2:5.55})

10.            Simulate threads using yield operator

^{JavaScript 1.7}

var scheduler = new function () {

  var _workers = [];

  this . Add = function ( worker ) {

    _workers . push ( new worker () );
  }

  this . Run = function () {

    while ( _workers . length )
      for each ( var worker in _workers )
        try {
          worker . next ();
        } catch ( err if err instanceof StopIteration ) {
          _workers . splice ( _workers . indexOf ( worker ), 1 );
        }
  }
}

function worker1 () {

  for ( var i = 0 ; i < 5 ; i ++ ) {

    Print ( 'worker1: ' + i , '/n' );
    yield ;
  }
}

scheduler . Add ( worker1 );

function worker2 () {

  for ( var i = 0 ; i < 10 ; i ++ ) {

    Print ( 'worker2: ' + i , '/n' );
    yield ;
  }
}

scheduler . Add ( worker2 );

scheduler . Run ();

prints:

worker1 : 0
worker2 : 0
worker1 : 1
worker2 : 1
worker1 : 2
worker2 : 2
worker1 : 3
worker2 : 3
worker1 : 4
worker2 : 4
worker2 : 5
worker2 : 6
worker2 : 7
worker2 : 8
worker2 : 9

11.            swap two variables

^{JavaScript 1.7}

var a = 1 ;
var b = 2 ;
[ a , b ] = [ b , a ];

12.            Destructuring assignment with function arguments

^{JavaScript 1.7}

function foo ( [ a , b ] ) {

        Print ( a );
        Print ( b );
}

foo ( [ 12 , 34 ] );

Prints:

12
34

13.            JavaScript scope and LET instruction

^{JavaScript 1.7}

var x = 5 ;
var y = 0 ;
let ( x = x + 10 , y = 12 ) {
  Print ( x + y );
}
Print ( x + y );

prints:

27
5

or,

for ( let i = 0 ; i < 10 ; i ++ ) {
  Print ( i + ' ' );
}
Print ( i );

prints:

0 1 2 3 4 5 6 7 8 9 test . js : 4 : ReferenceError : i is not defined

14.            Iterate on values

^{JavaScript 1.6}

for each ( var i in [ 3 , 23 , 4 ] )
        Print ( i )

Prints:

3
23
4