<!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
