方法1：arr.indexOf(element)：判斷數(shù)組中是否存在某個值，如果存在，則返回數(shù)組元素的下標(第一個元素)，否則返回-1；
let fruits = ["Banana","Orange","Apple","Mango"]
let a = fruits.indexOf("Apple")
console.log(a)// 2
方法2：array.includes(searcElement[,fromIndex])：判斷數(shù)組中是否存在某個值，如果存在返回true，否則返回false；
let fruits = ["Banana", "Orange", "Apple", "Mango"]
if(fruits.includes("Apple")){
console.log("存在")
}else {
console.log("不存在")
}
方法3：arr.find(callback[,thisArg])：返回數(shù)組中滿足條件的第一個元素的值，如果沒有，返回undefined；
let fruits = ["Banana","Orange","Apple","Mango"]
let result = fruits.find(item=>{
????return item =="Apple"
})
console.log(result)// Apple
方法4：array.findIndex(callback[,thisArg])：返回數(shù)組中滿足條件的第一個元素的下標，如果沒有找到，返回-1；
let fruits = ["Banana","Orange","Apple","Mango"]
let result = fruits.findIndex(item=>{
????return item =="Apple"
})
console.log(result)// 2
方法5：for()：遍歷數(shù)組，然后 if 判斷；
let fruits = ["Banana","Orange","Apple","Mango"]
for(v of fruits){
????if(v =="Apple"){
????????console.log("包含該元素")?
????}
}
方法6：forEach
let fruits = ["Banana","Orange","Apple","Mango"]
fruits.forEach((v)=>{
????if(v =="Apple"){
????????console.log("包含該元素")?
????}
})
