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Harmony Proxies in Node.js

simplereach
September 19, 2012

Harmony Proxies in Node.js

Russell Bradberry's presentation for the New York Node.js Meetup.

simplereach

September 19, 2012
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  1. Russell Bradberry @devdazed [email protected] H r Pr N JS

  2. E b H r Pr $ node --harmony-proxies

  3. W pr ? • Provides access to the hidden underlying

    methods of an object • Lets you define how the object will act • After created, object handlers are protected • Proxy.create(handler, proto) => Object instances • Proxy.createFunction(handler, callTrap, constructTrap) => Functions & Classes
  4. Tr p ( r) Required Traps Optional Traps • getOwnPropertyDescriptor

    • getPropertyDescriptor • getOwnPropertyNames • getPropertyNames • definProperty • delete • fix • has • hasOwn • get • set • enumerate • keys
  5. R q r Tr p • getOwnPropertyDescriptor => function(name){ ...

    } Object.getOwnPropertyDescriptor(obj, name); Return a property descriptor for the object • getPropertyDescriptor => function(name){ ... } (not in ES5) Doesn't exist in NodeJS (ES5) so use same definition as getOwnPropertyDescriptor • getOwnPropertyNames => function(){ ... } Object.getOwnPropertyNames(obj); Return a list of property names • getPropertyNames => function(){ ... } (not in ES5) Doesn't exist in NodeJS(ES5) so use same definition as getOwnPropertyNames • defineProperty => function(name, descriptor){ ... } What to do when someone does "proxy.foo = 'bar'" • delete => function(name) { ... } What to do when someone calls "delete proxy.foo" • fix => function(){ ... } What happens when you call Object[freeze|seal|preventExtensions](proxy)
  6. Op Tr p • has => function(name) { ... }

    Return a boolean indicating the key exists in the object Defaults to "name in obj" • hasOwn => function(name){ ... } Return a boolean if this property exists as an "own" object Defaults to "Object.prototype.hasOwnProperty.call(obj, name)" • get => function(receiver, name){ ... } Receiver is the proxy name is the method or property to get Defaults to "return myobj[name]" • set => function(receiver, name, value){ ... } Receiver is the proxy Name is the key being set Value is the value to set to Defaults to "myObj[name] = value" • enumerate => function(){ ... } Return an array of keys to enumerate over Defaults to "var a = []; for(var k in myObj){ a.push(k); } return a;" • keys => function(){ ... } What to return when Object.keys is called Defaults to "return Object.keys(myObj)"
  7. Pr . r var myObj = { foo:'bar', answer:null };

    var handler = { //forward all required traps to myObj get:function(rec, name){ return myObj[name] || function(){ console.log(name, 'is missing'); return undefined; } } }; var proxy = Proxy.create(handler, myObj); myObj.foo => 'bar' proxy.foo => 'bar' myObj.bar() => undefined > "bar is missing"
  8. Pr . r F var myObj = { foo:'bar' };

    var construct = function(){ this.baz = 'qux' }; var handler = { //forward all required traps to myObj }; var MyProxy = Proxy.createFunction(handler, construct); MyProxy.foo => 'bar' new MyProxy() => { baz: 'qux' }
  9. Pr Mocking JS Objects: • https://github.com/devdazed/supermock • Mocks anything •

    Any undefined property returns a new mock • Any undefined method also returns a new mock • Mocks are named according to their position in the object hierarchy • Built in assertion testing $ npm install supermock $ node --harmony-proxies > SuperMock = require('supermock').SuperMock > myMock = new SuperMock() [SuperMock: <anonymous>] > myMock.foo.bar.baz().qux.russ.is.awesome() [SuperMock: <anonymous>.foo.bar.baz().qux.russ.is.awesome()]
  10. Q ?

  11. :) Russell Bradberry @devdazed [email protected]