1 <!DOCTYPE html> 2 <html> 3 <head lang="en"> 4 <meta charset="UTF-8"> 5 <title></title> 6 </head> 7 <body> 8 <script> 9 10 var arr = ["a","b","c","d","c","b","a"]; 11 12 //indexOf从前往后给元素查索引，找到一个后，立刻返回。 13 console.log(arr.indexOf("a")); 14 console.log(arr.indexOf("b")); 15 console.log(arr.indexOf("x")); 16 17 //lastIndexOf从后往前给元素查索引，找到一个后，立刻返回。 18 console.log(arr.lastIndexOf("a")); 19 console.log(arr.lastIndexOf("b")); 20 console.log(arr.lastIndexOf("x")); 21 22 23 24 25 </script> 26 </body> 27 </html>