<button id="a" value="b" onClick="aoba()" name="botão"> BOTÃO 1 </button>
<script type="text/javascript">
  var x = document.getElementById('a').name;

 function aoba(){alert(x);};

</script>

function aoba(){
    var x = document.getElementById('a').name;
    alert(x);
}

<script type="text/javascript">
    var x;

    function aoba(){alert(x);};

    window.onload = function(){ // acrescenta o name em x quando a pagina terminar se ser carregada.
        x = document.getElementById('a').name;
    }

</script>

window.onload = function(){
    var x = document.getElementById('a').name;
    function aoba(){
        alert(x);
    };
}