Introduction
In your html page add the control you want to validate but for this sample I used textbox to demonstrate this code, in my textbox control i used onkeyup event to validate whether recently entered character is numeric or not. So you can call this JavaScript code as your requirement in your project.
Test.html
------------
<input type="text" id="txt" name="txt" onkeyup="txtValidate(this.id)"/>
JavaScript Code
-------------------
function txtValidate(txtid)
{
var ok=0;
var a=document.getElementById(txtid).value;
for(var i=0;i<=a.length-1;i++)
{
var j=a.charCodeAt(i);
for(var k=48;k<=57;k++)
{
ok=0;
if(k==j)
{
ok=1;
break ;
}
}
}
if(ok==0)
{
alert("Only Numeric Values Allowed");
document.getElementById(txtid).value="";
for(var i=0;i<a.length-1;i++)
{
var j=a.charCodeAt(i);
for(var k=48;k<=57;k++)
{
ok=0;
if(k==j)
{
document.getElementById(txtid).value+=a.charAt(i);
}
}
}
}
}