Tham khảo sách 'javascript bible_ chapter 22', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Text-Related Objects The Netscape document object model for forms includes four text-related input objects text password textarea and hidden. All four of these objects are used for entry display or temporary storage of text data. While all of these objects can have text placed in them by default as the page loads scripts can also modify the contents of these objects. Importantly all but the hidden objects retain their user- or script-modified content during a soft reload for example clicking the Reload button except in Internet Explorer 3. Hidden objects revert to their default values on all reloads in all browsers. A more obvious difference between the hidden object and the rest is that its invisibility removes it from the realm of user events and actions. Therefore only the text-style object properties apply to the hidden object. The persistence of text and textarea object data through reloads and window resizes makes these objects prime targets for off-screen storage of data that might otherwise be stored temporarily in a cookie. If you create a frame with no size for example you set the COLS or ROWS values of a FRAMESET tag to let all visible frames occupy 100 of the space and assign the rest to the hidden frame you can populate it with fields that act as shopping cart information or other data holders. Therefore if users have cookies turned off or don t usually respond affirmatively to cookie requests your application can still make use of temporary client storage. The field contents may survive unloading of the page but whether this happens and for how many navigations away from the page the contents last depends on the visitor s cache settings or if the browser is Internet Explorer 3 in which case no values preserve the unloading of a document . If the user quits Navigator the field entry is lost. In This Chapter Capturing and modifying text field contents Triggering action by entering text Capturing individual keystroke events 434 Part III JavaScript Object
