1.indexOf() -> ES5
const array = ['a', 'b', 'c']
array.indexOf('a') // 存在=>返回下标
array.indexOf('a') // 不存在=>返回-1
2.find() -> ES6
const array = ['a', 'b', 'c']
array.find(obj => obj == 'a') //存在=>返回数值a
array.find(obj => obj == 'a') //不存在=>返回undefined
const arrayList = [
{name: 'name1'}, {name: 'name2'}
]
arrayList.find(obj => obj.name == 'name1') //存在=>返回对象{name:'name1'}
arrayList.find(obj => obj.name == 'name1')//不存在=>返回undefined
3.findIndex() -> ES6
const array = ['a', 'b', 'c']
array.findIndex(obj => obj == 'a') //存在=>返回下标
array.findIndex(obj => obj == 'a')//不存在=>返回-1
4.includes()
const array = ['a', 'b', 'c']
array.includes('a') //存在=>返回true
array.includes('a') //不存在=>返回false
5.filter()
const array = ['a', 'b', 'c']
array.filter(obj => obj == 'a') //存在=>返回['a']
array.filter(obj => obj == 'a') //不存在=>返回[]
const array = [{ name: 'a' }, { name: 'a' }]
array.filter(obj => obj.name === 'a') //存在=>[{name: 'a'}]
array.filter(obj => obj.name === 'a') //不存在=>[]