Simply put, callback function: that is, the function to be executed.
(1) Definition of callback function
##
function add(x,y,fn) {
/*
* this.x this.y：属于add类的全局变量的定义
* */
this.x=x||1;
this.y=y||1;
if(fn){ /*判断是否有回调函数，有的话执行传入的函数（传入参数）*/
fn(this.x+this.y);
}
}2) The callback function is usually an anonymous function with a return value
## add(1,2,function (v) {//回调函数有返回值
if(v>0){
alert("result>0")
}else{
alert("result<0")
}
})Copy after login
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