Validate Phone or Fax Number using JavaScript

Introduction

This is a small JavaScript function that is useful for validating a phone/fax number. It gives an alert message if user enters data other than numbers.

Using the Code

We will create one JavaScript function called "ValidateNo".

In this function, there are two arguments:

1. NumStr: This is the value which you want to validate. It will come from your form control. It may by TextBox control (HTML or ServerControl).
2. String: This is a predefined format which you can use to validate phone/fax number. It may contain +, - and space. You can modify it as per your requirement.

Below is the JavaScript function ValidateNo, which we create for validation purpose.

function ValidateNo(NumStr, String)
{
    for(var Idx=0; Idx<NumStr.length; Idx++)
    {
        var Char = NumStr.charAt(Idx);
        var Match = false;

        for(var Idx1=0; Idx1<String.length; Idx1++)
        {
            if(Char == String.charAt (Idx1))
                Match = true;
        }

        if (!Match)
            return false;
    }
    return true;
}

We can put ValidateNo function in common JavaScript file, from where we can access it in all pages of the application.

Now we create one JavaScript function called "ValidateDetail".

function ValidateDetail()
{
    if(document.getElementById("phone").value == "")
    {
       alert("Please specify Phone number");
       document.getElementById("phone").focus();
       return false;
    }

    if(!ValidateNo(document.getElementById("phone").value,"1234567890"))
    {
        alert("Please enter only Number");
        document.getElementById("phone").focus();
        return false;
    }

    return true;
} 

Now you can call this JavaScript "ValidateDetail" function for validating your phone and fax number.