pattern: closure - singleton

 

var collection = (function() {

    // private members
    var objects = [];

    // public members
    return {
        addObject: function(object) {
            objects.push(object);
        },
        removeObject: function(object) {
            var index = objects.indexOf(object);
            if (index >= 0) {
                objects.splice(index, 1);
            }
        },
        getObjects: function() {
            return JSON.parse(JSON.stringify(objects));
        }
    };
})();

collection.addObject("Bob");
collection.addObject("Alice");
collection.addObject("Franck");
// prints ["Bob", "Alice", "Franck"]
console.log(collection.getObjects());
collection.removeObject("Alice");
// prints ["Bob", "Franck"]
console.log(collection.getObjects());

var namesCollection = (function() {
    // private members
    var objects = [];

    function addObject(object) {
        objects.push(object);
    }

    function removeObject(object) {
        var index = objects.indexOf(object);
        if (index >= 0) {
            objects.splice(index, 1);
        }
    }

    function getObjects() {
        return JSON.parse(JSON.stringify(objects));
    }

    // public members
    return {
        addName: addObject,
        removeName: removeObject,
        getNames: getObjects
    };
})();

namesCollection.addName("Bob");
namesCollection.addName("Alice");
namesCollection.addName("Franck");
// prints ["Bob", "Alice", "Franck"]
console.log(namesCollection.getNames());
namesCollection.removeName("Alice");
// prints ["Bob", "Franck"]
console.log(namesCollection.getNames());

var singleton = (function() {
    // private singleton value which gets initialized only once
    var config;

    function initializeConfiguration(values){
        this.randomNumber = Math.random();
        values = values || {};
        this.number = values.number || 5;
        this.size = values.size || 10;
    }

    // we export the centralized method for retrieving the singleton value
    return {
        getConfig: function(values) {
            // we initialize the singleton value only once
            if (config === undefined) {
                config = new initializeConfiguration(values);
            }

            // and return the same config value wherever it is asked for
            return config;
        }
    };
})();

var configObject = singleton.getConfig({ "size": 8 });
// prints number: 5, size: 8, randomNumber: someRandomDecimalValue
console.log(configObject);
var configObject1 = singleton.getConfig({ "number": 8 });
// prints number: 5, size: 8, randomNumber: same randomDecimalValue as in first config
console.log(configObject1);