January 2013
Intermediate to advanced
332 pages
5h 23m
Chinese
Content preview from JAVASCRIPT網頁應用程式設計
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44
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第三章
自動產生 ID
目前在儲存資料時，都得要自行設定一組 ID，這還蠻麻煩的。不過只要加點簡單的處
理，就能讓設定 ID 的工作變得自動化。首先，我們需要一種產生 ID 的機制，像是全
域唯一識別碼（Globally Unique Identifier，GUID）產生器就是一種不錯的選擇。不過
JavaScript 在技術上沒辦法產生真正 128 位元的 GUID—它只能產生出一些類似隨機的
亂數（pseudorandom）。因為要產生真正的 GUID 非常困難，需要透過作業系統取得網
卡 MAC 位址、滑鼠游標所在位置，以及 BIOS 檢查碼（checksums）…等資訊；更專業
一點的做法，可能還得量測電子雜訊、放射性衰變…等數據！ JavaScript 內建的
Math.
random()
函式，雖然只是類似隨機的亂數，但也足以滿足我們的需求。
Robert Kieffer 曾利用
Math.random()
開發出一個非常簡單的 GUID 產生器程式（
http://www.
broofa.com/2008/09/javascript-uuid-function/
）。它簡單到可以直接貼進我們的程式裡：
Math.guid = function(){
return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
var r = Math.random()*16|0, v = c == 'x' ? ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.