Introduction to apply and Math.max() functions in js

This article mainly introduces you to the problems of apply and Math.max() functions in js. At the bottom of the article, I mentioned the difference between Math.max.apply and Math.max in js. I hope it can help you.

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 me some advice from a js expert.

Answer 1

Function.apply() is an OOP feature of JS. It is generally used to simulate inheritance and extending this. For 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 a 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 The 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, ...])

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 Javascript

Javascript The Math.max method in 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.
Cleverly make arrays can also call Math.max and Math.min.

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

Related recommendations:

JavaScript call and apply

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