input angka

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>

<script>
function validAngka(txtbox){
    var isian = txtbox.value;
    var angka = '0123456789';
    var isAngka;
    for(var i=0; i<txtbox.value.length; i++) {
        isAngka=false;
        for(var j=0;j<angka.length;j++){
            if( txtbox.value.charAt(i) == angka.charAt(j) ) {
                isAngka=true;
            }
        }
        if(isAngka == false) {
            txtbox.value = txtbox.value.replace(txtbox.value.charAt(i), '');
            i--;
        }
    }

    return true;
}
</script>
</head>

<body>
<input type="txtbox" id="input_angka" name="input_angka" value="" onkeyup="validAngka(this)" />

</body>
</html>