上下文使用调用并在Javascript中应用？

问题描述

任何人都可以解释上下文在Javascript中使用 call 和 apply 方法吗？

为什么要使用调用和应用而不是直接调用函数？

解决方案

您使用或到功能。从本质上讲，这意味着您要执行一个函数，就好像它是特定对象的方法一样。两者之间的唯一区别是调用期望参数用逗号分隔，而 apply 期望数组中的参数。 / p>

来自，其中构造函数被链接：

  function产品（名称，价格）{
 this.name = name; 
 this.price = price; 
 
 if（price< 0）
抛出RangeError（'无法创建产品''+名+'，负价格'）; 
返回此; 
} 
 
函数食品（名称，价格）{
 Product.apply（this，arguments）; 
 this.category ='food'; 
} 
 Food.prototype = new Product（）; 
 
函数玩具（名称，价格）{
 Product.apply（this，arguments）; 
 this.category ='toy'; 
} 
 Toy.prototype = new Product（）; 
 
 var cheese = new Food（'feta'，5）; 
 var fun = new Toy（'机器人'，40）; 
  

什么 Product.apply（this，arguments）确实如下： Product 构造函数作为函数应用于每个 Food 和<$ c $中c>玩具构造函数，并且每个对象实例都以此的形式传递。因此，每个食物和玩具现在都有 this.name 和 this.category 属性。

Guys can any one explain context to use call and apply methods in Javascript?

Why to use call and apply instead of calling a function directly ?

解决方案

You use call or apply when you want to pass a different this value to the function. In essence, this means that you want to execute a function as if it were a method of a particular object. The only difference between the two is that call expects parameters separated by commas, while apply expects parameters in an array.

An example from Mozilla's apply page, where constructors are chained:

function Product(name, price) {
    this.name = name;
    this.price = price;

    if (price < 0)
        throw RangeError('Cannot create product "' + name + '" with a negative price');
    return this;
}

function Food(name, price) {
    Product.apply(this, arguments);
    this.category = 'food';
}
Food.prototype = new Product();

function Toy(name, price) {
    Product.apply(this, arguments);
    this.category = 'toy';
}
Toy.prototype = new Product();

var cheese = new Food('feta', 5);
var fun = new Toy('robot', 40);

What Product.apply(this, arguments) does is the following: The Product constructor is applied as a function within each of the Food and Toy constructors, and each of these object instances are being passed as this. Thus, each of Food and Toy now have this.name and this.category properties.

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