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);

 

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