在文本框中设置最后一个字符后的焦点

I have 3 text boxes for a phone number. As the user types, it automatically moves from one textbox to the next. When the user presses backspace, I can move focus to the previous text box. The problem is that in IE, focus is set to the beginning of the text box. Here's my code, which works fine in chrome.I have 3 text boxes for a phone number. As the