js中的this关键字，setTimeout(),setInterval()的执行过程

windseek

发布于 2018-06-14 09:44:30

1.3K00

代码可运行

运行总次数：0

代码可运行

var test1 = {
name: 'windseek1',
showname: function () {
console.log(this.name);
}
}
var test2 = {

name:'windseek2',
showname: test1.showname
}
test2.showname()

运算结果是windseek2，由于test2.showname=test1.showname所以test2.showname()=test1.showname();

test2.showname=

function () {

console.log(this.name);

}

test2.showname();对象时test2，所以this也指向test2 name自然也是test2.name windseek2

上面的代码也相当于这样写：

var test1 = {
name: 'windseek1',
showname: function () {
console.log(this.name);
}
}
var test2 = {

name:'windseek2',
showname: function () {
console.log(this.name);
}
}
test2.showname()

运算结果是一样的

var test1 = {
name: 'windseek1',
showname: function () {
console.log(this.name);
}
}
var test2 = {

name:'windseek2',
showname: function () {
test1.showname();
}
}
test2.showname()

这时的运算结果应该是windseek1，由于test2.showname()执行其实是找到，test1.showname()执行，对象时test1，this指向test1，结果也就是test1.name也就是windseek1

var name="windseek";
var test1 = {
name: 'windseek1',
showname: function () {
console.log(this.name);
}
}
var test2 = {

name:'windseek2',
showname: function () {
var test=test1.showname;
test();
}
}
test2.showname();

结果是windseek，因为test2.showname()执行时会找到test()执行，test=function () {console.log(this.name);},test前面没有任何对象，作用域就是全局的，this就是全局变量，this.name也就是windseek

上述代码可以解释成以下代码

var name="windseek";
var test1 = {
name: 'windseek1',
showname: function () {
console.log(this.name);
}
}
var test2 = {

name:'windseek2',
showname: function () {
var test=function () {
console.log(this.name);
};
test();
}
}
( function () {
var test=function () {
console.log(this.name);
};
test();
})();

写到这，感觉写代码像是在做数学题了，越来越有意思了

var name='windseek';
var test1 = {
name: 'windseek1',
showname: function () {
console.log(this.name);
}
}
var test2 = {

name:'windseek2',
showname: function () {
setTimeout(test1.showname,1000);
}
}
test2.showname();

结果就是windseek其实，setTimeout等价于这种函数function(__callback){ __callback();} 最后执行的是callback

等价于这样写

var name='windseek';
var test1 = {
name: 'windseek1',
showname: function () {
console.log(this.name);
}
}
var test2 = {

name:'windseek2',
showname: function () {
(function(__callback){
    __callback();
})(test1.showname);
}
}
test2.showname();