focus next input when maxlength is reached

nextField.js

var a = document.getElementById('form:tabView:kan1'),
	b = document.getElementById('form:tabView:kan2'),
	c = document.getElementById('form:tabView:jahr');
		
a.onkeyup = function() {
	if (this.value.length === parseInt(this.attributes["maxlength"].value)) {
		b.focus();
	}
}
			
b.onkeyup = function() {
	if (this.value.length === parseInt(this.attributes["maxlength"].value)) {
		c.focus();
	}
}