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 in5)
 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');

functionThrowAnError(){

  (function(){

    thrownewError("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 =newfunction(){

  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 instanceofStopIteration){
          _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:

0123456789 test.js:4:ReferenceError: i isnotdefined

14.            Iterate on values

^{JavaScript 1.6}

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

Prints:

3
23
4