gipi的學習筆記-經營管理、數據思考、終身學習

InfoQ：ECMAScript 5 released，這篇來自InfoQ的文章中指出，ECMAScript 5已經推出了，這個版本終於將Javascript的鬆散結構做了一些改善，強制規定某些程式的寫法，真的算是一件好事阿，以下列舉他提到的幾個點，感覺起來確實有將過去很惹人厭，造成不好維護，不好偵錯的一些問題做了改善：

• Variables must be declared before use. In other words, i=3 becomes a runtime error; var i=3 is needed (assuming i is not in scope at the time)
• Eval becomes a reserved word, and introducing new variables through eval cannot occur, so eval("var i=3"); print(i); will now throw an error.
• Octal literals are no longer used; so 010 is ten, and not eight
• delete cannot be used against arguments, functions or variables or other properties with the configurable flag set to false
• with statements, often a source of errors, are no longer used and considered syntax errors
• Functions can no longer have duplicate arguments with the same name
• Objects can no longer have duplicate properties with the same name
• The arguments and caller variables become immutable
• Access to the global object becomes a runtime error

 

另外也提供了許多基本函式，第一項就是前陣子大家在討論的日期format，也加入了物件列舉功能，希望他的加強不只這些吧：

• Date now supports the ability to generate ISO8601 formatted dates (such as 20091209T12:34:56Z) as well as to parse them
• String now has a built-in trim() method
• A new JSON object with parse and stringify to support efficient generation of JSON data; like eval but without the security implications of being able to reduce code. In addition, any JSONValue can be used, not just JSONObject and JSONArray as specified in RFC 4627. (4627 defines JSON-Text to be constrained to an object or array.)
• A new bind builtin has been added, with the same semantics as Prototype's bind()
• Array now has standard functions, such as indexOf(), map(), filter(), and reduce()
• Object now has seal() (which prevents new properties being added or existing properties deleted) and freeze() (which makes all properties read-only, as well as preventing new properties being added or deleted)
• Object.keys() lists all the enumerable properties of the object
• Object.getOwnPropertyNames() lists all the enumerable and non-enumerable properties
• Object.getPrototypeof() returns the prototype of the given object

 

ECMAScript 5原則上應該還可以期待，目前只希望它的向下相容性是高的，避免我們之前寫的code要全面改版，這就很痛苦了。

 

參考資料：

ECMAScript 5 Objects and Properties

InfoQ：ECMAScript 5 released

EcmaScript 5: Changes to JavaScript

游舒帆 (gipi) 探索原力Co-founder，曾任TutorABC協理與鼎新電腦總監，並曾獲選兩屆微軟最有價值專家 ( MVP )，離開職場後創辦探索原力，致力於協助青少年培養面對未來的能力。認為教育與組織育才其實息息相關，都是在為未來儲備能量，2018年起成立為期一年的專題課程《職涯躍升的關鍵24堂課》，為培養台灣未來的領袖而努力。