js闭包

//闭包引起的bug
function bug() {
 ???var nums = [];
 ???for (var i = 0; i < 3; i++) {
 ???????nums[i] = function () {
 ???????????return i;
 ???????};
 ???}
 ???return nums;
}
var nums_bug = bug();
console.log(nums_bug[0]());
console.log(nums_bug[1]());
console.log(nums_bug[2]());
//修复bug
function fbug() {
 ???var nums = [];
 ???for (var i = 0; i < 3; i++) {
 ???????nums[i] = (function (i) {
 ???????????return i;
 ???????})(i);
 ???}
 ???return nums;
}
var nums = fbug();
console.log(nums);
//nums[0](); 0
//nums[1](); 1
//nums[2](); 2

//隔离变量作用域
(function(){
 ???var name = "zs";
 ???function a(){
 ???????name = ‘sss‘;
 ???}
})();
(function(){
 ???var name = "ls";
 ???function a(){
 ???????name = ‘vvv‘;
 ???}
})();

//计数器
//普通实现
var num = 0;
function countNum(){
 ???num ++;
}
countNum();
console.log(num);
//闭包实现
var counter = (function(){
 ???var counterPer = 0;
 ???return function(){
 ???????return counterPer++;
 ???}
})();
console.log(counter());

var counter=(function(){
 ???//赋初值
 ???var count=0;
 ???//外部调用时形成闭包
 ???return function(){
 ???????return count++;
 ???}
})();
//声明私有变量

/*function People(){
 ???this.name = ‘张三‘;
}
var p = new People();
console.log(p.name);*/
//直接可以.来进行访问，这是公有属性，安全性差
//私有属性是通过.访问不到的

var People = (function(){
 ???var name = ‘‘;
 ???function People(){

 ???}
 ???People.prototype = {
 ???????getName : function(){
 ???????????return name;
 ???????},
 ???????setName : function(newName){
 ???????????name = newName;
 ???????}
 ???}
 ???return People;
})();
var p = new People();

//this
var test = ‘李四‘;
function th_test(){
 ???console.log(this.test);
}

function bth_test(){
 ???var test = ‘王五‘;
return function(){
 ???console.log(this.test);
}
}
//this永远指向调用它的对象