How to determine whether an array contains an element

Use findIndex
Definition and Usage ：
findIndex() Method returns a test condition passed in （ function ） The first element position of the qualified array .

There are two points to pay attention to ：

1. When an element in an array tests a condition, it returns true when , findIndex() Returns the index position of a qualified element , Subsequent values do not call the execute function . Example 2 Is a good illustration , Even in the back 666 and 66 Greater than 50, But it only found 99, The following loop will not be executed .
2. If no eligible element returns -1

example 1：

let allList=[1,2,3,4,5];
let d = allList.findIndex(item=>item==5) //4.

example 2：

var arr2 = [1,18,2,99,666,44,66];
    var flag2 = arr2.findIndex(item => {
    
        return item > 50;
    });
    console.log(flag2) // 3

find Method ： Find out the qualified elements in the elements

let allList=[{
    id:1,name:' Winter rain '},{
    id:2,name:" Wintersweet "}];
let d = allList.find(item=>item.id==1)
console.log(d);// { id: 1, name: ' Winter rain ' }


let allList=[{
    id:1,name:' Winter rain '},{
    id:2,name:" Wintersweet "}];
let d = allList.find(item=>item.id==5)
console.log(d);//undefined