how to find out html textfield field focus in .js file

i want find html textf开发者_如何学Cield blur or focus through .js file

---

Are you looking for javascript events?

onFocus, onBlur and onChange

The onFocus, onBlur and onChange events are often used in combination with validation of form fields.

Source: http://www.w3schools.com/JS/js_events.asp