detectar tecla intro pulsada en javascript

<script>

//***********************************
function pulsadoIntro(e)
{

    tecla = document.all ? e.keyCode : e.which;

    if (tecla==13)
    {
        //enviar();
        alert('hola');
    }

}

</script>


(...)

<input type="text" name="nombre" style="width: 200px;" onkeypress="pulsadoIntro(event);">




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