Javascript调用和应用方法

Question

I am confused by this code:

Function.prototype.apply.call(Math.floor, undefined, [1.75]); // 1

I read this post javascript apply and call methods and chain together and I understand the meaning of chaining apply and call methods together.

However, I am still confused about the syntax. The correct syntax for call is function.call(thisArg, arg1, arg2, ...) . But in this case, why could the call method take these three parameters ( target , thisArgument , argumentsList ), which is the same as Reflect.apply(target, thisArgument, argumentsList) ?

Answer 1

Actually, call method can take all comma separated arguments and pass it to the called method. While as you see here (target, thisArgument, argumentsList) Second two arguments work as arguments for apply method and we know that apply method gonna need an array of argument, we have sent third parameter as an array.

So here the execution can be simplified to :

Math.floor.apply(undefined, [1.75]);

Or simply Math.floor(1.75) // Obv with undefined as reference of this

Answer 2

    Function.prototype.apply.call(Math.max, undefined, [1,75]); // 1

code above change thisArgu in Function.prototype.apply to Math.max

let's talk about change thisArgu in Function.prototype.apply to Math.max

noramlly, this in Function.prototype.apply should be Function.prototype

so change thisArgu in Function.prototype.apply to Math.max means:

change Function.prototype to Math.max if met 'this' when executing in Function.prototype.apply()

so code above can be understood like this when execute and meet 'this' :

    Math.max.apply(undefined,[1,75])

now you understand?

if we go on ,you will find

    Math.max.apply(undefined,[1,75])

can be understood like:

    Window.max(1,75)//error;

so , i guess 'this' word doesn't exist in Math.max function content,so it gets no error;

Answer 3

The syntax for call() is:

someFunctionOrMethod.call(...)

So, this code is calling the apply method of the Function type.

// Call the "apply()" method
Function.prototype.apply.call()

// With the following arguments passed to "apply"
(Math.floor, undefined, [1.75])