tailieunhanh - Học JavaScript qua ví dụ part 50

Xử lý sự kiện Giới thiệu cho người xử lý sự kiện JavaScript phản ứng với các sự kiện. Chúng tôi đã nói về sự kiện kể từ khi Chương 1, "Giới thiệu về JavaScript," bởi vì sự kiện này vốn là một phần của hầu như tất cả các trang web và họ làm cho các trang tương tác và năng động. JavaScript sự kiện không đồng bộ, có nghĩa là họ có thể xảy ra bất cứ lúc nào. Họ là những hành động được khởi xướng bởi một người dùng truy cập vào một trang web, ví dụ, nếu. | chapter 13 Handling Events Introduction to Event Handlers JavaScript reacts to events. We have been talking about events since Chapter 1 Introduction to JavaScript because events are inherently part of almost all Web pages and they make the pages interactive and dynamic. JavaScript events are asynchronous meaning that they can happen at any time. They are actions that are initiated by a user visiting a Web page for example if the user submits a form or moves the mouse over a link or an image he or she might trigger an event. When an event occurs your browser has some default actions it takes for example if you click on a link it opens up the location in the href. JavaScript can also respond to a user s action and execute code in response. The event itself may be blur click change keystroke and so on. We have seen many examples using event handlers in previous examples. This chapter explains how each of the event handlers responds when events occur on different objects. JavaScript has three event models for programming events the inline model the scripting model and the DOM 2 model. In this chapter we discuss the inline model and the scripting model. In Chapter 15 The W3C DOM and JavaScript we describe the way events are handled by the W3C DOM Level 2 model and its pros and cons. The Inline Model for Handling Events This is the oldest and easiest way to handle events. With the inline model the event handlers are attributes of an HTML tag and are used to handle the event for which they are named. For example the onClick handler will handle the click event the onSubmit handler will handle the submit event and so on. Although a very popular way of dealing with events the disadvantage of using the inline model is that JavaScript is intrusive that is it is not separated from the HTML markup. The inline model will be used here to show you what the many event handlers do and how they affect the objects in a document. Later in this chapter we discuss the .