js文本框焦点自动聚焦到下个文本框

HTML：

<form>
　　<input type="text" name="text1" maxlength="3" size="3"/>-
　　<input type="text" name="text2" maxlength="3" size="3"/>-
　　<input type="text" name="text3" maxlength="3" size="3"/>
</form>

js：

function tabForward() {
    if(this.value.length == this.getAttribute('maxlength')) {
        for(let i = 0;i < this.form.elements.length;i ++) {
            if(this == this.form.elements[i]) {
                if(this.form.elements[i + 1]) {
                    this.form.elements[i + 1].focus();
                    return;
                }
            }
        }
    }
}
var form = document.forms[0];
var text1 = form.elements['text1'];
var text2 = form.elements['text2'];
var text3 = form.elements['text3'];
text1.addEventListener('keyup', tabForward, false);
text2.addEventListener('keyup', tabForward, false);
text3.addEventListener('keyup', tabForward, false);