How can I insert Numeric Values only in a textbox ?

Java Script for Insert Numeric Values only.

function IsNumeric(txtvalue)
{
if (txtvalue.value != "")
{
if (isNaN(txtvalue.value))
{
alert("Please Enter Numeric Value")
txtvalue.focus();
txtvalue.value = "";
return false;
}
}
}

call this function on text box onblur event type:- onblur=txtphone_no(this);

hope this will help the freshers.