HTML5使用ApplicationCache接口实现离线缓存技术解决离线难题

APPCACHE 事件
正如您所预期的那样，附加事件会用于监听缓存的状态。浏览器会对下载进度、应用缓存更新和错误状态等情况触发相应事件。以下代码段为每种缓存事件类型设置了事件监听器：

复制代码
function handleCacheEvent(e) {
//...
}
function handleCacheError(e) {
alert('Error: Cache failed to update!');
};
// Fired after the first cache of the manifest.
appCache.addEventListener('cached', handleCacheEvent, false);
// Checking for an update. Always the first event fired in the sequence.
appCache.addEventListener('checking', handleCacheEvent, false);
// An update was found. The browser is fetching resources.
appCache.addEventListener('downloading', handleCacheEvent, false);
// The manifest returns 404 or 410, the download failed,
// or the manifest changed while the download was in progress.
appCache.addEventListener('error', handleCacheError, false);
// Fired after the first download of the manifest.
appCache.addEventListener('noupdate', handleCacheEvent, false);
// Fired if the manifest file returns a 404 or 410.
// This results in the application cache being deleted.
appCache.addEventListener('obsolete', handleCacheEvent, false);
// Fired for each resource listed in the manifest as it is being fetched.
appCache.addEventListener('progress', handleCacheEvent, false);
// Fired when the manifest resources have been newly redownloaded.
appCache.addEventListener('updateready', handleCacheEvent, false);

如果清单文件或其中指定的资源无法下载，整个更新都将失败。在这种情况下，浏览器将继续使用原应用缓存