javascript_design_patterns/ObserverPattern.js at master · colbisaurusrex/javascript_design_patterns · GitHub

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/* Observer Pattern */

/* -------- Observer List------- */

function ObserverList() {

this.observerList = [];

}

ObserverList.prototype.Add = function(obj) {

return this.observerList.push(obj);

};

ObserverList.prototype.Empty = function() {

this.observerList = [];

};

ObserverList.prototype.Count = function() {

return this.observerList.length;

};

ObserverList.prototype.Get = function(index) {

if (index > -1 && index < this.observerList.length) {

return this.observerList[index];

}

};

ObserverList.prototype.Insert = function(obj, index) {

var pointer = -1;

if (index === 0) {

this.observerList.unshift(object);

pointer = index;

} else if (index === this.observerList.length) {

this.observerList.push(obj);

pointer = index;

}

return pointer;

};

ObserverList.prototype.IndexOf = function(obj, startIndex) {

var i = startIndex,

pointer = -1;

while (i < this.observerList.length) {

if (this.observerList[i] === obj) {

pointer = i;

}

i++;

}

return pointer;

};

ObserverList.prototype.RemoveAt = function(index) {

if (index === 0) {

this.observerList.shift();

} else if (index === this.observerList.length - 1) {

this.observerList.pop();

}

};

// I guess this is a simple utility and not intended to be a method of ObserverList

function extend(extension, obj) {

for (var key in extension) {

obj[key] = extension[key];

}

/* -------- Subject ------- */

function Subject() {

this.observers = new ObserverList();

}

Subject.prototype.AddObserver = function(observer) {

this.observers.Add(observer);

};

Subject.prototype.RemoveObserver = function(observer) {

this.observers.RemoveAt(this.observerList.IndexOf(observer, 0));

};

Subject.prototype.Notify = function(context) {

var observerCount = this.observers.Count();

for (var i = 0; i < observerCount; i++) {

this.observers.Get(i).Update(context);

}

};

/* -------- Observer ------- */

function Observer() {

this.Update = function() {}

}

Notes:

- The Observer is a design pattern in which an object (known as a subject) maintains a list of objects depending on it (observers), automatically notifying them of any changes to state

- Requires that the observer(or object) wishing to receive topic notifications must subscribe this intererest to the object firing the event (the subject)

javascript_design_patterns/ObserverPattern.js at master · colbisaurusrex/javascript_design_patterns · GitHub

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