SOURCE

let uid = 0;
export default class Dep {
    constructor() {
        this.id = uid++;
        this.subs = [];
    }
    addSub(sub) {
        this.subs.push(sub);
    }
    removeSub(sub) {
        remove(this.subs, sub);
    }
    depend() {
        if (window.target) {
            window.target.addDep(this);
        }
    };
    removeSub(sub) {
        const index = this.subs.indexOf(sub);
        if (index > -1) {
            return this.subs.splice(index, 1);
        }
    }
    notify() {
        const subs = this.subs.slice();
        for (let i = 0, l = subs.length; i < l; i++) {
            subs[i].update();
        }
    }
}