JavaScript - 闭包

理解

• 关于闭包

function fun(n, o) {
    console.log(o);
    return {
        fun: function (m) {
            return fun(m, n);
        }
    }
}
var a = fun(0);
a.fun(1);
a.fun(2);
a.fun(3);
var b = fun(0).fun(1).fun(2).fun(3);
var c = fun(0).fun(1);
c.fun(2);
c.fun(3);

答案:

 undefined
 0
 0
 0
 undefined
 0
 1
 2
 undefined
 0
 1
 1

用arguments.callee和闭包实现的函数封装

var data = [];
for (var i = 0; i < 3; i++) {
  (data[i] = function () {
    console.log(arguments.callee.i);//此处i不是外部i
  }).i = i;
}
data[0](); //0
data[1](); //1
data[2](); //2

应用

• 利用闭包实现自动递增计数

var countNumber = (function() {
    var num = 0;
    return function() {
        return ++num;
    }
})();
console.log(countNumber());//1
console.log(countNumber());//2
console.log(countNumber());//3
console.log(countNumber());//4