observers.js

function observer() {
    const data = {};
    const callbacksObj = {};
    const set = (property, value) => {
        data[property] = value;
        notify(property);
    };
    const notify = (property) => {
        if(!property) {
            throw new TypeError('Property "property" is not type string')
        }
        if (callbacksObj[property]) {
            callbacksObj[property]
                .forEach((callback) => {
                    callback();
                });
        }
        return true;
    };
    const subscribe = (property, callback) => {
        if(!property && typeof property !== 'string') {
            throw new TypeError('Property "property" is not type string')
        }
        if(!callback) {
            throw new TypeError('Property Callback is not type function');
        }
        if(callbacksObj[property]) {
            callbacksObj[property].push(callback.bind(null, data));
        }
        callbacksObj[property] = [];
        callbacksObj[property].push(callback.bind(null, data));
    };

    return {
        subscribe,
        set,
    }
}