includes
存在返回true,否则返回false
indexOf:
返回给定元素的第一个索引，没有返回-1
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<script>
let a = ['tom','jeck','jep','jeck']
console.log(a.includes('jeck'))
console.log(a.includes('jj'))
console.log(a.indexOf('jj'))
console.log(a.indexOf('jeck'))
</script>
</body>
</html>
