Simple ES Javascript Plugin for Data Manager & Observer (Single state of truth)

ssz_data_manager_observer.js

window.DataManager = {
	setData: function ( data ) {

        if ( typeof data !== 'object' ) {
            throw new Error( 'Only accept object!' );
        }

        var hashPrevData = JSON.stringify( DataManager.data );
        var hashData = JSON.stringify( data );

        if ( hashPrevData !== hashData ) {
            DataManager._prevData = _.cloneDeep( DataManager._data );
            DataManager._data = _.merge( DataManager.data, data );
            for ( var i in DataManager.observer ) {
                var observeCallback = DataManager.observer[ i ];
                observeCallback( DataManager.data, DataManager.prevData );
            }
        }
	},
	get data() {
		return DataManager._data;
	},
	get prevData() {
		return DataManager._prevData;
	},
	set observer( callback ) {
		if ( typeof callback !== 'function' ) {
			throw new Error( 'Only accept function!' );
		}
		DataManager._observers.push( callback );
	},
	get observer() {
		return DataManager._observers;
	},
	_observers: [],
	_data: {},
	_prevData: {}
};

// Example register `observer` callback
DataManager.observer = function( data, prev ) {

	// example usage with previous data
	if ( prev.name ) {
		console.log( 'Bye ' + prev.name + '!' );
	} 

	console.log( 'Hello ' + data.name + '!' );
};

// Example set data
DataManager.setData( { name: 'Syaiful' } );
// Hello Syaiful!

// Example set data and use previous data
DataManager.setData( { name: 'Arifah' } );
// Bye Syaiful!
// Hello Arifah!