# Validating user input in JavaScript

Many developers may face a big problem while dealing with JavaScript; it’s the problem of validating user input using REGULAR EXPRESSIONS

Here are simple steps to do so:

-First what is a regular expression?!

It’s a tool for performing pattern matches and it has to categories

1-literal syntax , it’s something like that

var reg = /pattern/<br />


2-Dynamic regular expression that can be done using the RegExp() constructor , it’s something like that

var reg = new RegExp("pattern") ;<br />


after we have got a regular expression we can use it any where

and here’s an example that may be helpful

-In this example we insure that the user enters 6 digits.

first i’ll construct an html form like that

<html>
<script type="text/javascript"></script>

<body>
<form name="iForm">
<input type="text" name="iText" />
<button onclick="validateInput();">Click Me</button>
</form>
</body>
</html>


and between the script tags we put our JavaScript code the will get the job done

function validateInput()
{
var reg = /^\d{6}$/ if(document.iForm.iText.value.search(reg)==-1) { alert("Wrong input.....Please Enter Valid input !!!!") } }  Here i’ll reveal some mysterious about the previous expression ^ this means that it will start comparing from the first digit d{6} means that it will do comparing for 6 digits $ means that it must be 6 digits till the end of the input(actually $means the end of the input) here’s another trick if you want to validate email input from the user we can do this with this function function validateInput() { var reg = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/
if(document.iForm.iText.value.search(reg)==-1)
{