IE8/IE9 in JavaScript does not support Array.indexof solutions

Scene:
JS determines whether a string is in an array of JS.
Method:

The code is as follows	Copy Code
if ([' A ', ' B ', ' C '].indexof (str) >= 0) { Do something }

Determines whether the name of the selected file has an extension in the specified array:

The code is as follows	Copy Code
var position = Selectedfilepath.lastindexof ("."); if (position<=0) { Alert ("Do not allow uploading of files of this extension!") "); Return } else{ var ext = selectedfilepath.substr (position); ext = Ext.tolowercase (); var Extarr = [". jpg", ". png", ". gif", ". jpeg"]; if (extarr.indexof (EXT) = =-1) { Alert ("Do not allow uploading of files of this extension!") "); Return } }

Issue: IE9 The following version does not support [].indexof ()
Solution

Create your own indexof functions for IE8 and the following versions.
Ie8.js:

The code is as follows

Copy Code

if (! Array.prototype.indexOf) {   Array.prototype.indexOf = function (ELT/*, from*/)   {  & nbsp;  var len = this.length >>> 0;     var from = number (Arguments[1]) | | 0;     from = (from < 0)         ? Math.ceil (from)         : Math.floor (from);     if ( From < 0)       from = len;     for (; from < Len; from++)     {       if (from I n this &&           this[from] = = ELT)          return from;    }     return-1;  }; }

Then introduce ie8.js in the relevant pages

The code is as follows	Copy Code
<!--[If Lt IE 9]> <script src= "Https://oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js" ></script> <script src= "Https://oss.maxcdn.com/libs/respond.js/1.4.2/respond.min.js" ></script> <script src= "./assets/js/ie8.js" ></script> <! [endif]-->