javascript闭包

理解了下面几个例子，对于闭包，应该可以算是入门了。

 

  1.

 

  function say667() {

    var num = 666;

    var sayAlert = function() { alert(num); }

    num++;

    return sayAlert;

  }

 

  var sayAlert = say667();

  sayAlert();

 

  2.

 

  function setUpSomeGlobals() {

    var num = 666;

    gAlertNumber = function() { alert(num); }

    gIncreaseNumber = function() { num++; }

    gSetNumber = function(x) { num = x; }

  }

 

  setUpSomeGlobals();  //为三个全局变量赋值

  gAlertNumber();  //666

  gIncreaseNumber();  

  gAlertNumber();  //667

  gSetNumber(12);

  gAlertNumber();  //12

 

  3.

 

  function buildList(list) {

    var result = [];

    for(var i = 0; i < list.length; i++) {

      var iteml = 'item' + list[i];

      result.push( function() { alert(item + ' ' + list[i]); });

    }

    return result;

  }

 

  function testList() {

    var fnlist = buildList([1, 2, 3]);

    for(var j = 0; j < fnlist.length; j++) {

      fnlist[j]();

    }

  }

 

  4.

 

  function sayAlice() {

    var sayAlert = function() { alert(alice); }

    var alice = 'Hello Alice';

    return sayAlert;

  }

 

  var helloAlice = sayAlice();

  helloAlice();  //Hello Alice

 

  5.

 

  function newClosure(someNum, someRef) {

    var num = someNum;

    var anArray = [1,2,3];

    var ref = someRef;

    return function(x) {

      num += x;

      anArray.push(num);

      alert('num: ' + num + '\nanArray ' + anArray.toString() + '\nref.someVar ' + ref.someVar);

    }  

  }

 

  closure1 = newClosure(40, { someVar: 'closure 1'});

  closure2 = newClosure(1000,{ someVar: 'closure 2'});

 

  closure1(5);

  closure2(-10);