Editing Observer pattern (section)

===JavaScript===

JavaScript has a deprecated {{code|Object.observe}} function that was a more accurate implementation of the observer pattern.<ref>{{Cite web|url=https://stackoverflow.com/a/50862441/887092|title = jQuery - Listening for variable changes in JavaScript}}</ref> This would fire events upon change to the observed object. Without the deprecated {{code|Object.observe}} function, the pattern may be implemented with more explicit code:<ref>{{Cite web|url=https://stackoverflow.com/a/37403125/887092|title = Jquery - Listening for variable changes in JavaScript}}</ref>

<syntaxhighlight lang="js">
let Subject = {
    _state: 0,
    _observers: [],
    add: function(observer) {
        this._observers.push(observer);
    },
    getState: function() {
        return this._state;
    },
    setState: function(value) {
        this._state = value;
        for (let i = 0; i < this._observers.length; i++)
        {
            this._observers[i].signal(this);
        }
    }
};

let Observer = {
    signal: function(subject) {
        let currentValue = subject.getState();
        console.log(currentValue);
    }
}

Subject.add(Observer);
Subject.setState(10);
//Output in console.log - 10
</syntaxhighlight>