js闭包

Posted 2020-10-27 剑域柳

//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