Javascript snippets

JavascriptSnippets.js

// Summation of two variables

let firstName = 'John',
    lastName = 'Doe';

let greeting = `Hi ${firstName}, ${lastName}`;
console.log(greeting); // Hi John, Doe

// Observer

class Observer {
    constructor() {
        this.listeners = [];
    }
    addListener(name, callback) {
        let id = {};
        this.listeners.push({ id, name, callback });
        return id;
    }
    addOnceListener(name, callback) {
        let id = {};
        this.listeners.push({
            id, name, callback: () => {
                callback();
                this.removeListener(id);
            }
        });
        return id;
    }
    removeListener(id) { this.listeners = this.listeners.filter(it => it.id != id); }
    dispatch(name, ...args) {
        this.listeners.filter(it => it.name == name).forEach(it => it.callback(...args));
    }
}