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使用 indexOf 方法,返回查找元素在数组中第一次出现位置(下标值),否则返回-1
var a=["1", "3", "2", "3", "0"]; console.log(a.indexOf ('3'));//1console.log(a.indexOf (5,'0'));//-1console.log(a.indexOf ('0'));//4console.log(a.indexOf ('0',-5));//4console.log(a.indexOf ('3',-1));//-1console.log(a.indexOf ('3',-3));//3console.log(a.indexOf ('1',5));//-1console.log(a.indexOf (3));//-1 console.log(a);//["1", "3", "2", "3", "0"]
属于ES语法,使用 includes 方法,返回值是布尔类型
let arr = [1,2,3];arr.includes(1) // truearr.includes(5) //false
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