Validacion onkeypress

[uselox]

Nueva Funcion:

Código Javascript:

var validarNum = function (event, _float){
    event = event || window.event;
    var charCode = event.keyCode || event.which;
    var first = (charCode <= 57 && charCode >= 49);
    if(_float){
        var element = event.srcElement || event.target;
        return first || (element.value.indexOf('.') == -1 ? charCode == 46 : false);
    }
    return first;
}
 

...

Código HTML:

<!-- no decimales -->
<input type="text" onkeypress="validarNum(event)"/>

<!-- con decimales -->
<input type="text" onkeypress="validarNum(event, true)"/>