Judgment method: 1. Use "arr.includes(value)", if it returns true, it exists; 2. Use "arr.find(function(v){if(v==value{//true }})" statement; 3. Use "arr.some(i=>i===value)", if it returns true, it exists.

Method 1: Use the includes method of es6
includes() method is used to determine whether an array contains a specified value and returns true or false. Syntax:array.includes(searchElement, fromIndex);
- searchElement: the element to be found;
- fromIndex: the index position to start searching.
arr = [1,2,3,4,5] console.log(arr.includes(5));

5 is in the array.
Method 2 : Use the find method of es6
find() method returns the value of the first element of the array that passes the test (judged within the function).find() method is in the array Each element of Call the execution function.- If there is no element that meets the conditions, return undefined
- Example:
var arr = [1,2,3,4,5] arr.find(function(value){ if(value==5){ console.log("指定元素在数组中"); } })

arr = [1,2,3,4,5]; let istrue= arr.some(item => item === 45); console.log(istrue);
You can see that the return value is false, which means the element is not in the array.
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