onchange javascript

HTML

<form action="">
    <input type="text" name="mal" id="mal" maxlength="3"
    onkeyup="checkMax(this);">Male<br>
    <input type="text" name="fem" id="fem" maxlength="3">Female<br>
    <input id="1" type="text" onchange="ValidatePassKey(this)" maxlength="4">
<input id="2" type="text" onchange="ValidatePassKey(this)" maxlength="4">
<input id="3" type="text" onchange="ValidatePassKey(this)" maxlength="4">
<input id="4" type="text" maxlength="4">
</form>

JavaScript

var radios= document.getElementsByTagName('input');
var mal= document.getElementById("mal").value;
var fem= document.getElementById("fem").value;


function checkMax (element) {
	if (element.value.length == element.maxlength)
		document.getElementById('fem').focus();
}

function ValidatePassKey(tb) {
  if (tb.TextLength >= 4)
    document.getElementById(tb.id + 1).focus();
}