每個函數都包含兩個非繼承而來的方法:call()和apply();
在JavaScript中,call和apply作用是一樣的,都是爲了改變某個函數運行時的上下文(context)而存在的,換句話說,就是爲了改變函數體內部this的指向。
function fruits(){}
fruits.prototype = {
color: "red",
say: function(){
console.log("My color is " + this.color);
}
};
var apple = new fruits;
apple.say(); //My color is red
當想另外一個對象想使用fruits中的say方法時不用重新寫,使用call和apply可以實現“劫持”別人的方法。
function fruits(){}
fruits.prototype = {
color: "red",
say: function(){
console.log("My color is " + this.color);
}
};
var another = {
color: "yellow"
};
var apple = new fruits;
apple.say(); //My color is red
apple.say.call(another); //My color is yellow
apple.say.apply(another); //My color is yellow
區別:參數書寫方式不同
call(thisObj, arg1, arg2, arg3, arg4);
apply(thisObj, [args]);
thisObj:call和apply第一個參數是一樣的,該參數將替代Function類裏面的this對象。
arg1,arg2....:是一個個的參數,
args:一個數組或類數組,是一個參數列表。
用法
var name = "小白";
var obj = {
name: "小紅"
};
function sayName() {
return this.name;
}
console.log(sayName.call(this)); //小白
console.log(sayName.call(obj)); //小紅
實現繼承
//實現js繼承
//父類
function Person(name, height) {
this.sayInfo = function() {
return "姓名:" + name + ", 身高:" + height + ", 體重:" + this.weight;
}
}
//子類
function Chinese(name, height, weight) {
Person.call(this, name, height);
this.weight = weight;
this.nation = function() {
console.log("我是中國人");
}
}
//子類
function America(name, height, weight) {
Person.call(this, name, height); //America 繼承了 Person的方法,簡單的說,就是把Person的方法全放到了 America
this.weight = weight;
}
let chiness = new Chinese("成龍", "178cm", "60kg");
console.log(chiness.sayInfo()); //姓名:成龍, 身高:178cm, 體重:60kg
let america = new America("jack", "180cm", "55kg");
console.log(america.sayInfo()); //姓名:jack, 身高:180cm, 體重:55kg
本篇文章是借鑑的,因爲寫的不錯,冒犯之處,請見諒