ES6 in Node.js

All ECMAScript 2015(ES6) features are split into three groups for shipping, staged, and in progress features.

  1. Shipping: are turned on by default on Node.js

  2. Staged: –es_staging or –harmony to open the feature

  3. In progress: –harmoney_destructuring, although this is highly discouraged unless for testing purposes.

    You may list all the in progress features avaliable on each Node.js release by grepping through the –v8-options argument.

    Please note that these are incomplete and possibly broken features of V8, so use them at your own risk:

    node –v8-options grep “in progress”

JavaScript ECMA-262 specification

  • Notes –harmony flag one Node.js is to enable staged features only , If you want to play safe, especially on production environments, consider remove this runtime flag until it ships by default on V8 and, consequently, on Node.js. If you keep this enabled, your should be prepared for further Node.js

    upgrades to break your code if V8 changes their semantics to more closely follow the standard.

  • Find the version of V8 ships with the current version of Node.js

    node -p process.versions.v8

Guids

  • Easy profiling for Node.js Applications

    There are many third party tools available for profiling Node.js applcaiton , but in many cases, theeasiest option is to use the Node.js

    built in profiler, The built in profiler uses the profiler inside V8, In the past you need

    the V8 source code to be able to interpret the ticks. Luckily, tools have recently been introduced into Node.js 4.1.1 that facilitate the consumptions of this

    information without separetely building V8 from source .

     NODE_ENV=production node --prof app.js

 curl -X GET "http://localhost:8080/newUser?username=matt&password=password"

 ab -k -c 20 -n 250 "http://localhost:8080/auth?username=matt&password=password"

 node <path_to_nodejs_src>/tools/v8-prof/tick-processor.js isolate-0x101804c00-v8.log >processed.txt

  • Working with Different Filesystems.

    1. Case Preservation You may create a directory called test/abc and be surprised to see sometimes that fs.readdir(‘test’) returns [‘ABC’]. This is not a bug in Node. Node returns the filename as the filesystem stores it, and not all filesystems support case-preservation. Some filesystems convert all filenames to uppercase (or lowercase).

    2. Unicode Form Preservation You may create a directory called test/café (NFC Unicode form with byte sequence <63 61 66 c3 a9> and string.length === 5) and be surprised to see sometimes that fs.readdir(‘test’) returns [‘café’] (NFD Unicode form with byte sequence <63 61 66 65 cc 81> and string.length === 6). This is not a bug in Node. Node returns the filename as the filesystem stores it, and not all filesystems support Unicode form preservation.

    3. Comparing Different Unicode Forms string1.normalize(‘NFC’) === string2.normalize(‘NFC’)

    4. Timestamp Resolution You may set the mtime (the modified time) of a file to 1444291759414 (millisecond resolution) and be surprised to see sometimes that fs.stat returns the new mtime as 1444291759000 (1-second resolution) or 1444291758000 (2-second resolution). This is not a bug in Node. Node returns the timestamp as the filesystem stores it, and not all filesystems support nanosecond, millisecond or 1-second timestamp resolution. Some filesystems even have very coarse resolution for the atime timestamp in particular,

Node.JS 5.1.0 Api Documentation

QA

  • 关于严格模式

类和模块的内部，默认就是严格模式，所以不需要使用use strict指定运行模式。只要你的代码写在类或模块之中，就只有严格模式可用。 考虑到未来所有的代码，其实都是运行在模块之中，所以ES6实际上把整个语言升级到了严格模式。

  • 关于子类

任何一个子类都有constructor方法。

constructor(…args) { super(…args); }

  • 类的prototype属性和__proto__属性

大多数浏览器的ES5实现之中，每一个对象都有__proto__属性，指向对应的构造函数的prototype属性。Class作为构造函数的语法糖，同时有prototype属性和__proto__属性，因此同时存在两条继承链。

（1）子类的__proto__属性，表示构造函数的继承，总是指向父类。

（2）子类prototype属性的__proto__属性，表示方法的继承，总是指向父类的prototype属性。 ``` class A { }

class B { }

// B的实例继承A的实例 Object.setPrototypeOf(B.prototype, A.prototype);

// B继承A的静态属性 Object.setPrototypeOf(B, A); 《对象的扩展》一章给出过Object.setPrototypeOf方法的实现。

Object.setPrototypeOf = function (obj, proto) { obj.proto = proto; return obj; }

B.prototype = new A(); // 等同于 B.prototype.proto = A.prototype;

```

  • 原生构造函数的继承

Boolean() Number() String() Array() Date() Function() RegExp() Error() Object()

ES6可以自定义原生数据结构（比如Array、String等）的子类，这是ES5无法做到的。