Use of apply+Math.max() function
This time I will bring you the use of the apply Math.max() function and what are the precautions for using the apply Math.max() function. The following is a practical case, let’s take a look.
Let me introduce to you the problems of apply and Math.max() functions in js. The specific contents are as follows:
var arr=[1,3,6,3,7,9,2]; console.log(Math.max.apply(null,arr));
I still don’t understand why the maximum value of an array can be calculated in this way? 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. 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)
< -1But 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
I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!
Recommended reading:
How to pass an array to the background controller
How to customize the operation login form code in Vue.js
The above is the detailed content of Use of apply+Math.max() function. For more information, please follow other related articles on the PHP Chinese website!
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