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<html><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Keywords" name="Keywords"content="JavaScript, examples, JavaScript: The Definitive Guide"><title>Example 19-3 from JavaScript: The Definitive Guide, Fifth Edition</title><style>body { font-family: arial, sans-serif}.lefttitle { font: bold x-small arial, sans-serif; margin: 5px; letter-spacing: .15em; text-transform:uppercase;}.leftcaption { font: italic x-small sans-serif; margin-bottom: 20px;}#banner { font-family:sans-serif; color:#333; font-size:x-large; font-weight:normal; padding:15px; padding-top: 3px; border-bottom:4px double #666;}#banner h1 { font-size: x-large; margin: 0px; padding: 0px;}#banner .description { font-size:large; margin-left: 2px;}pre { border: solid black 1px; background-color: #ddd; padding: 10px; margin: 0px;} </style></script></head><body><div id="banner"><h1>davidflanagan.com/javascript5</h1><span class="description">Example 19-3 from<i>JavaScript: The Definitive Guide, Fifth Edition</i></span></div><div style="float: left; 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text-align: right"><a href="index.html" tppabs="http://www.davidflanagan.com/javascript5/index.html">Table of Examples</a></div><pre>/** * PObject.js: JavaScript objects that persist across browser sessions and may * be shared by web pages within the same directory on the same host. * * This module defines a PObject() constructor to create a persistent object. * PObject objects have two public methods. save() saves, or "persists" the * current properties of the object, and forget() deletes the persistent * properties of the object. To define a persistent property in a PObject, * simply set the property on the object as if it were a regular JavaScript * object and then call the save() method to save the current state of * the object. You may not use "save" or "forget" as a property name, nor * any property whose name begins with $. PObject is intended for use with * property values of type string. You may also save properties of type * boolean and number, but these will be converted to strings when retrieved. * * When a PObject is created, the persistent data is read and stored in the * newly created object as regular JavaScript properties, and you can use the * PObject just as you would use a regular JavaScript object. Note, however * that persistent properties may not be ready when the PObject() constructor * returns, and you should wait for asynchronous notification using an onload * handler function that you pass to the constructor. * * Constructor: * PObject(name, defaults, onload): * * Arguments: * * name A name that identifies this persistent object. A single pages * can have more than one PObject, and PObjects are accessible * to all pages within the same directory, so this name should * be unique within the directory. If this argument is null or * is not specified, the filename (but not directory) of the * containing web page is used. * * defaults An optional JavaScript object. When no saved value for the * persistent object can be found (which happens when a PObject * is created for the first time), the properties of this object * are copied into the newly created PObject. * * onload The function to call (asynchronously) when persistent values * have been loaded into the PObject and are ready for use. * This function is invoked with two arguments: a reference * to the PObject and the PObject name. This function is * called *after* the PObject() constructor returns. PObject * properties should not be used before this. * * Method PObject.save(lifetimeInDays): * Persist the properties of a PObject. This method saves the properties of * the PObject, ensuring that they persist for at least the specified * number of days. * * Method PObject.forget(): * Delete the properties of the PObject. Then save this "empty" PObject to * persistent storage and, if possible, cause the persistent store to expire. * * Implementation Notes: * * This module defines a single PObject API but provides three distinct * implementations of that API. In Internet Explorer, the IE-specific * "UserData" persistence mechanism is used. On any other browser that has a * Macromedia Flash plugin, the Flash SharedObject persistence mechanism is * used. Browsers that are not IE and do not have Flash available fall back on * a cookie-based implementation. Note that the Flash implementation does not * support expiration dates for saved data, so data stored with that * implementation persists until deleted. * * Sharing of PObjects: * * Data stored with a PObject on one page is also available to other pages * within the same directory of the same web server. When the cookie * implementation is used, pages in subdirectories can read (but not write) * the properties of PObjects created in parent directories. When the Flash * implementation is used, any page on the web server can access the shared * data if it cheats and uses a modified version of this module. * * Distinct web browser applications store their cookies separately and * persistent data stored using cookies in one browser is not accessible using * a different browser. If two browsers both use the same installation of * the Flash plugin, however, these browsers may share persistent data stored * with the Flash implementation. * * Security Notes: * * Data saved through a PObject is stored unencrypted on the user's hard disk. * Applications running on the computer can access the data, so PObject is * not suitable for storing sensitive information such as credit card numbers, * passwords, or financial account numbers. */// This is the constructorfunction PObject(name, defaults, onload) { if (!name) { // If no name was specified, use the last component of the URL name = window.location.pathname; var pos = name.lastIndexOf("/"); if (pos != -1) name = name.substring(pos+1); } this.$name = name; // Remember our name?? 快捷鍵說明
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