<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>funciton</title>
</head>
<body>
<script>
const arr=[1,,,,2,3,,4,,,,5,6,,,7,,,8,9]
arr.foreach(item=>{
console.log(item)//直接打印1,2,3,4,5,6,7,8,9
})
arr.find(item=>{
console.log(item) //，都是undefined
})
</script>
</body>
</html>
打印出值
Array.from.length //1
