Question: I am uploading images for our application to the server. 
Is there any way to validate the extensions in client side by JS before submitting them to the server before uploading them to server?

I am using AngularJs to handle my front-end.

Answer: 
You can use this simple javascript to validate. This code should be put inside a directive and on change of file upload control.

```
var extn = filename.split(".").pop();

```

Alternatively you can use javascript substring method also:

```
fileName.substr(fileName.lastIndexOf('.')+1)

```
You can create a angular directive, something like this should work (Change the accepted values in the validFormats array);

HTML:

```
    <form name='fileForm' >
        <input type="file" name="file" ng-model="fileForm.file" validfile>
    </form>

```

Javascript:

```
angular.module('appname').directive('validfile', function validFile() {

    var validFormats = ['jpg', 'gif'];
    return {
        require: 'ngModel',
        link: function (scope, elem, attrs, ctrl) {
            ctrl.$validators.validFile = function() {
                elem.on('change', function () {
                   var value = elem.val(),
                       ext = value.substring(value.lastIndexOf('.') + 1).toLowerCase();   

                   return validFormats.indexOf(ext) !== -1;
                });
           };
        }
    };
});

```