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October 13, 2015 16:35
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JavaScript OOP Design Pattern - Observer Pattern
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//observer pattern | |
//convert Subject into constructor function as there can be more than 1 | |
var Subject = function () { | |
var observerCollection = [], | |
subject = { | |
"registerObservers": function ( observerArr ) { | |
observerArr.forEach( addToRegister ); | |
return true; | |
}, | |
"unregisterObserver": function ( observer ) { | |
observerCollection.splice( observer.getID(), 1 ); | |
return true; | |
}, | |
"notify": function () { | |
observerCollection.forEach( fireNotify ); | |
} | |
}, | |
addToRegister = function ( subscriber, i ) { | |
assignID( subscriber, observerCollection.length );//added here to assign 0 | |
observerCollection.push( subscriber ); | |
}, | |
assignID = function ( o, id ) { | |
o.addID( id ); | |
}, | |
fireNotify = function ( observer, i ) { | |
observer.notify(); | |
}; | |
return subject; | |
}; | |
//constructor pattern used over revealing module pattern as there will be | |
//N instances of observers | |
function Observer () { | |
this.addID = function ( id ) { | |
if ( ! this._id ) { | |
this._id = id; | |
return true; | |
} | |
}; | |
this.getID = function () { | |
if ( this._id ) { | |
return this._id; | |
} | |
}; | |
this.notify = function () { | |
}; | |
} | |
var subject = Subject(), | |
observer1 = new Observer(), | |
observer2 = new Observer(), | |
observer3 = new Observer(), | |
observer4 = new Observer(); | |
//concrete notify() implementations | |
observer1.notify = function () { | |
console.log( "1" ); | |
}; | |
observer2.notify = function () { | |
console.log( "2" ); | |
}; | |
observer3.notify = function () { | |
console.log( "3" ); | |
}; | |
observer4.notify = function () { | |
console.log( "4" ); | |
}; | |
//register subscribers/observers | |
subject.registerObservers( [ observer1, observer2, observer3, observer4 ] ); | |
//fire notification w/ observer #3 | |
subject.notify(); | |
//unregister observer #3 | |
subject.unregisterObserver( observer3 ); | |
//fire notification w/o observer #3 | |
subject.notify(); |
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