Harmony Proxies in Node.js

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

Transcript

1. Russell Bradberry
   @devdazed
   rbradberry@simplereach.com
   H r Pr N JS
   

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

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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
   

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4. Tr p ( r)
   Required Traps Optional Traps
   • getOwnPropertyDescriptor
   • getPropertyDescriptor
   • getOwnPropertyNames
   • getPropertyNames
   • definProperty
   • delete
   • fix
   • has
   • hasOwn
   • get
   • set
   • enumerate
   • keys
   

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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)
   

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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)"
   

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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"
   

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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' }
   

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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: ]
   > myMock.foo.bar.baz().qux.russ.is.awesome()
   [SuperMock: .foo.bar.baz().qux.russ.is.awesome()]
   

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10. Q ?
    

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11. :)
    Russell Bradberry
    @devdazed
    rbradberry@simplereach.com
    

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