@web-native-js/observer/src/observer/closure.js

A simple set of functions for intercepting and observing JavaScript objects and arrays.

/**
 * @imports
 */
import _copy from '@webqit/util/obj/copy.js';
import _unique from '@webqit/util/arr/unique.js';
import _isTypeObject from '@webqit/util/js/isTypeObject.js';
import _isArray from '@webqit/util/js/isArray.js';
import getObservers from './getObservers.js';
import unlink from './unlink.js';
import link from './link.js';

/**
 * Executes a callback function on a subject in "closure" mode.
 * Fires any observers that may be bound to subject on recorded changes.
 *
 * @param function		callback
 * @param array			...subjects
 *
 * @return array|Event
 */
export default function(callback, ...subjects) {
	var context = subjects.map(subject => {
		if (!_isTypeObject(subject)) {
			throw new Error('Target must be of type object!');
		}
		return {
			subject,
			subjectCopy: _isArray(subject) ? subject.slice(0) : _copy(subject),
		};
	});
	// ---------------------------------
	var result = callback(...subjects);
	// ---------------------------------
	context.map(cntxt => {
		var initialKeys = Object.keys(cntxt.subjectCopy);
		var currentKeys = Object.keys(cntxt.subject);
		var related = [];
		var changes = _unique(initialKeys.concat(currentKeys)).map(key => {
			if (cntxt.subjectCopy[key] !== cntxt.subject[key]) {
				related.push(key);
				// ---------------------------------
				// The event object
				var e = {
					name:key,
					related,
					buffered: true,
				};
				if (currentKeys.includes(key)) {
					e.type = 'set';
					e.value = cntxt.subject[key];
					if (initialKeys.includes(key)) {
						e.isUpdate = true;
					}
				} else {
					e.type = 'del';
				}
				if (initialKeys.includes(key)) {
					e.oldValue = cntxt.subjectCopy[key];
				}
				// ---------------------------------
				// Unobserve outgoing value for bubbling
				if (_isTypeObject(cntxt.subjectCopy[key])) {
					unlink(cntxt.subject, key, cntxt.subjectCopy[key]);
				}
				// Observe incoming value for bubbling
				if (_isTypeObject(cntxt.subject[key])) {
					link(cntxt.subject, key, cntxt.subject[key]);
				}
				return e;
			}
		}).filter(c => c);
		// ---------------------------------
		var observers;
		if (changes.length && (observers = getObservers(cntxt.subject, false))) {
			return observers.fire(changes);
		}
	});
	return result;
}