JavaScript implements the publish subscribe model

    /*Subject is the observed and notifies all observers of any changes in its state */
    class Subject {
        constructor(){
                this.state = "Initial state";
                this.observers = [];// Store all observers, and notify all observers when their state changes
                this.addobserver = function (observertmp) {
                    this.observers.push(observertmp);
                }
                this.changeState = function (data) {
                    console.log("State changed, notify all subscribers (observers)");
                    for(let i=0; i<this.observers.length; i++){this.observers[i].update(data);
                    }
                    this.state = data; }}}// An Observer is an Observer, and when changed by the Observer, the Observer calls its Update method
    class Observer{
            constructor(){
                this.update = function(data){
                    console.log("Observer: Found state changed, new state value is"+data); }}}let observerOne = new Observer();
    let observerTwo = new Observer();
    let subject = new Subject();
    subject.addobserver(observerOne);
    subject.addobserver(observerTwo);

    /* The observed state changes */
    subject.changeState("new state");
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Once the observed state changes, all observers will receive the new state: