apply和call的用法和区别.md

[nicoleJT914]

apply和call都是为了改变函数运行时的上下文而存在的，即改变函数体内部this的指向

区别：

• apply将参数作为数组传入
• call要将参数显示列出

  
  theFunction.apply(valueForThis, arrayOfArgs)
  theFunction.call(valueForThis, arg1, arg2, ...)

function theFunction(name, profession) { console.log("My name is " + name + " and I am a " + profession + "."); } theFunction("John", "fireman"); theFunction.apply(undefined, ["Susan", "school teacher"]); theFunction.call(undefined, "Claude", "mathematician"); theFunction.call(undefined, ...["Matthew", "physicist"]); // Output:

// My name is John and I am a fireman. // My name is Susan and I am a school teacher. // My name is Claude and I am a mathematician. // My name is Matthew and I am a physicist.

记忆法：A for array and C for comma

使用场景：当一个object没有某个方法，但是其他的有，我们可以借助call或apply用其它对象的方法来操作。
```js
function Cat() {
}
Cat.prototype = {
  food: 'fish',
  say: function() {
    console.log('I love ' + this.food)
  }
}
var cat = new Cat()
cat.say()  // I love fish

function Dog() {
}
Dog.prototype = {
  food: 'bone'
}
var dog1 = new Dog()
cat.say.call(dog1)  // I love bone

var dog2 = {
  food: 'beef'
}
cat.say.call(dog2)  // I love beef

参考：

• 如何理解和熟练运用js中的call及apply？
• What is the difference between call and apply?

[nicoleJT914]

bind实现

JavaScript深入之bind的模拟实现