用CustomerValidator 来验证 FileUpload控件的方法

How to check the FileUpload control on Client code(Brower)
First the FileUpload control is support Validator control
so we can use RegularExpressionValidator, CustomerValidator, because we can't set Ignore case property on Regular Expression Validator , so  i like use CustomerValidator to check the Extension.
The code on below, you can copy the code block to your page, and add one CustomerValidator

 <script type="text/javascript">
function CheckFile(sender,arg)
{
    var enableExt =["jpg","gif","bmp","png"]; // add your enable extension on that
    if (arg.Value=="")
    {
        arg.IsValid =true;
    }
    else
    {
        var temp = arg.Value.split(".");
        var extension = temp[temp.length-1];
        extension = extension.toLowerCase();
        var isValid = false;
        
        for(i=0;i<enableExt.length;i++)
        {
           if (extension==enableExt[i])
           {
                isValid=true;
           }
        }
        arg.IsValid = isValid;
    }
}
</script>