<body>
<input type="text" id="inp">
</body>
<script>
var SPACE_KEYCODE = 32;
document.getElementById('inp').onkeypress = function(eve) {
if ((eve.keyCode < 48 || eve.keyCode > 57) && eve.keyCode != SPACE_KEYCODE) {
return false;
}
this.value = this.value.replace(/\s+?/g, '*');
}
</script>