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

时间:2022-11-15 01:17:59
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();

结果一样也是windseek,但是这个不会延迟,settimeout会延迟,setInterval也是一样的原理