How to filter extension file using fileupload?

function CheckFileExistence()

{

var filePath=document.getElementById('<%= this.filUpload.ClientID %>').value;
if(filePath.length<1)

{
alert("File Name Can not be empty");return false;

}


var validExtensions = new Array();var ext = filePath.substring(filePath.lastIndexOf('.') + 1).toLowerCase();



validExtensions[0] = 'jpg';
validExtensions[1] = 'jpeg';

validExtensions[2] = 'bmp';
validExtensions[3] = 'png';

validExtensions[4] = 'gif';
validExtensions[5] = 'tif'; validExtensions[6] = 'eps';



for(var i = 0; i < validExtensions.length; i++) {
if(ext == validExtensions[i])return true;

}

alert('The file extension ' + ext.toUpperCase() + ' is not allowed!');
return false;

}


use the function into button like OnClientClick="return CheckFileExistence()"