//作用域鏈  var a = 1;  function test() {    var b =2;    return a;  }  alert(test());//彈出1；  alert(b);//不能獲取b//scope chain  var a = 1;  function test() {    var b = 2;    function test1() {      var c = 3;      alert(a);      alert(b);      alert(c);    }    test1();  }  test();//彈出1，彈出2，彈出3；

//詞法作用域；  function f1() {    var a = 12;    return f2();  }  function f2() {    return a;  }  alert(f1());//并不能獲取a，a在f2()中并未定義；function f1() {    var a = 1;    return f2();  }  function f2() {    var b = 3;    alert(b);    return a;  }  alert(f1());//彈出3，a在f2()中未定義function f1() {    var a = 1;    return f2();  }  function f2() {    var b = 3;    alert(b);    return a;  }  alert(f1());//彈出3，a在f2()中未定義,undefined  var a=55;  alert(f1());//彈出3，彈出55

//通過(guò)閉包突破全局作用域鏈  function f() {    var a = "sun";    return function () {      return a;    }  }  var test = f();  alert(test());//彈出sunvar n;function f() {  var a = "sun";  n = function () {    return a;  }}f();alert(n());//彈出sun  function f(param) {    var n =function () {      return param;    };    param++;    return n;  }  var test = f(45);  alert(test());//彈出46；