相信每一個開發者都知道緩存的重要性。從頭至尾有緩存的後台(memcached,xcache等。) 來減輕db的壓力。對內容分發網絡（CDN）緩存中希望你的浏覽器緩存那些不止一次的加載資源。當然, 有客戶端緩存,所以你不要重復昂貴的操作(即使是算法或大量的運算)。
這是介紹的是一個不錯的javascript的方面的客戶端解決方案,可選配支持HTML5本地存儲器.
Starting Simple
復制代碼 代碼如下:
function CacheProvider() {
// values will be stored here
this._cache = {};
}Feature detect on local storage
try {
CacheProvider.hasLocalStorage = ('localStorage' in window) && window['localStorage'] !== null;
} catch (ex) {
CacheProvider.hasLocalStorage = false;
}
這裡使用try catch的主要原因是 盡管firefox支持該屬性，但是需要在about:config中設置並開啟，否則將會報錯。所以一個簡單的if else不能滿足需求。
下面我們將增加對象本地存儲機制的支持。這個技術是借鑒了Christopher Blizzard的一篇不錯的文章 Saving data with local storage – for which those who didn't know, you can only store string's into local storage. Thus we have this…
in / out JSON parsing
復制代碼 代碼如下:
if (CacheProvider.hasLocalStorage) {
Storage.prototype.setObject = function(key, value) {
this.setItem(key, JSON.stringify(value));
};
Storage.prototype.getObject = function(key) {
return JSON.parse(this.getItem(key));
};
}
現在就到了我們的三個核心方法了，分別是 get, set, 和clear.
Core class functionality
復制代碼 代碼如下:
CacheProvider.prototype = {
/**
* {String} k - the key
* {Boolean} local - get this from local storage?
* {Boolean} o - is the value you put in local storage an object?
*/
get: function(k, local, o) {
if (local && CacheProvider.hasLocalStorage) {
var action = o ? 'getObject' : 'getItem';
return localStorage[action](k) || undefined;
} else {
return this._cache[k] || undefined;
}
},
/**
* {String} k - the key
* {Object} v - any kind of value you want to store
* however only objects and strings are allowed in local storage
* {Boolean} local - put this in local storage
*/
set: function(k, v, local) {
if (local && CacheProvider.hasLocalStorage) {
if (typeof v !== 'string')) {
// make assumption if it's not a string, then we're storing an object
localStorage.setObject(k, v);
} else {
try {
localStorage.setItem(k, v);
} catch (ex) {
if (ex.name == 'QUOTA_EXCEEDED_ERR') {
// developer needs to figure out what to start invalidating
throw new Exception(v);
return;
}
}
}
} else {
// put in our local object
this._cache[k] = v;
}
// return our newly cached item
return v;
},
/**
* {String} k - the key
* {Boolean} local - put this in local storage
* {Boolean} o - is this an object you want to put in local storage?
*/
clear: function(k, local, o) {
if (local && CacheProvider.hasLocalStorage) {
localStorage.removeItem(k);
}
// delete in both caches - doesn't hurt.
delete this._cache[k];
}
};
如何運用？
注意在這篇文章的開始，就說了Cache Provider 是可選支配的本地存儲，首先然讓我們看一個沒有本地存儲的例子：
getElementsByClassName
復制代碼 代碼如下:
var cache = new CacheProvider;
window.getElementsByClassName = getElementsByClassName || function(c) {
var reg = cache.get(c) || cache.set(c, new RegExp("(?:^|s+)" + c + "(?:s+|$)"));
var elements = document.getElementsByTagName('*');
var results = [];
for (var i = 0; i < elements.length; i++) {
if (elements[i].className.match(reg)) {
results.push(elements[i]);
}
}
return results;
};
備注：下次你調用類函數的時候， 將會用預先編譯好的正則表達式替代夠建造一個表達式。
再舉一個例子：比如 對於大的應用程序需要i18n，你可以緩存一個編譯好的html字符串進入本地存儲中。
復制代碼 代碼如下:
var i18nCache = new CacheProvider;
if (i18nCache.get('topnav')) {
$('#nav').html(i18nCache.get('topnav'));
} else {
ajax('top-nav.tmpl', function(html) {
i18nCache.set('topnav', html);
$('#nav').html(i18nCache.get('topnav'));
});
}
除此之外，你開可以做很多外部資源緩存到本地的事情，加油:)