The usage and difference between apply and Math.max()

This time I will bring you the use and difference between apply and Math.max(), what are the precautions about the use and difference between apply and Math.max(), the following is a practical case, let’s take a look one time.

var arr=[1,3,6,3,7,9,2];
console.log(Math.max.apply(null,arr));

I still don’t understand why this can calculate the maximum value of an array? I still can't figure it out, please give some advice from a js expert.

Answer 1

Function.apply() is an OOP feature of JS, generally used to simulate inheritance and Extending the purpose of this, the above code can be understood like this:

XXX.apply is a method of calling a function, and its parameters are: apply(Function, Args),

Function is the method to be called, Args is the parameter list, when Function is null, the default is as above,
that is,

Math.max.apply(null, arr)

can be considered as

apply(Math.max, arr)

Then, arr is a parameter list , for the max method, its parameters are several numbers, that is,

Math.max(a, b, c, d, ...)

When using apply, add all parameters to an array, that is,

arr = [a, b, c, d, ...]

is substituted into the original formula,

Math.max.apply(null, [a, b, c, d, ...])

is actually equivalent to

Math.max(a, b, c, d, ...)

Here, the advantage of using apply is to improve performance in some JS engines.

Answer 2

Math.max() method supports passing multiple parameters, such as: Math.max(1,4,2,3,7,5,6)

But it does not support directly passing an array as a parameter, such as: Math.max(new Array( 1,4,2,3,7,5,6)).

Here, as long as we have a way to split the array one by one and pass it to the Math.max() method, the method of passing the array is implemented.

All functions have the apply (scope chain, parameter) method. The "parameter" of this function receives an array, and separates each value in the array and passes it to the caller

Supplement: The difference between Math.max.apply and Math.max in

The Math.max method in Javascript can find the largest number among the given parameters.

> Math.max('1','2','3.1','3.2')
< 3.2
> Math.min(1,0,-1)
< -1

But if it is an array, it cannot be called like this.

The apply method is used at this time:

apply 方法 (Function) (JavaScript)
调用函数，并用指定对象替换函数的 this 值，同时用指定数组替换函数的参数。
apply([thisObj[,argArray]])
thisObj
　　可选。 要用作 this 对象的对象。
argArray

Optional. A set of arguments to be passed to the function.

> Math.max.apply(null, ['1','2','3.1','3.2'])
< 3.2
> Math.min.apply(null, [1,0,-1])
< -1

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