Validation in textbox only accept number using javascrit

function validate(key)

{
//getting key code of pressed key
var keycode = (key.which) ? key.which : key.keyCode;
var phn = document.getElementById('txtPhn');
//comparing pressed keycodes
if ((keycode < 48 || keycode > 57))
{
return false;
}


else
{

//Condition to check textbox contains ten numbers or not
if (phn.value.length <10)
{
return true;
}
else
{
return false;
}
}
}