lazy-aggregator/source/index.js

Creates aggregation wrapper

'use strict';
const add = Symbol.for('add');
const del = Symbol.for('del');

const handler = Symbol.for('handler');
const instances = Symbol.for('instances');

module.exports = class {
	/**
	 * Create lazy-initialized dictionary based on `source` dictionary handled with `fn`
	 * @constructor lazy-aggregator
	 * @param {Object.<string, *>} [source={}] - dictionary of configs for `fn` call
	 * @param {function} [fn=function(key,value){return value}] - function which will be used to create elements in aggregation
	 * @throws {Error} - if `fn` is not a function
	 * @example
	 * import Aggregation from 'lazy-aggregator';
	 * const fn = (a) => a * 2;
	 * const source = { el1: 1, el2: 2};
	 *
	 * const aggregation = new Aggregation(source, fn);
	 * aggregation['el1']; // 1
	 * aggregation.el2; // 2
	 */
	constructor(source = {}, fn = (key, value) => value) {
		this[handler] = fn;
		this[instances] = {};

		Object
			.entries(source)
			.forEach(([key, value]) => this[add](key, value));
	}

	/**
	 * add element to aggregation
	 * @param {String} key - first argument to `fn`
	 * @param {*} [value] - data for `fn` call
	 * @returns {Object} this
	 * @example
	 * import Aggregation from 'lazy-aggregator';
	 * import {add} from 'lazy-aggregator';
	 * const fn = (a) => a * 2;
	 * const source = { el1: 1, el2: 2};
	 * const aggregation = new Aggregation({}, fn);
	 * aggregation[add]('newEl', 2);
	 * aggregation.newEl; // 4
	 */
	[add](key, value) {
		Object.defineProperty(this, key, {
			get: () =>
				this[instances][key] ?
					this[instances][key] :
					this[instances][key] = this[handler](key, value)
			,
			set: function (value) {
				this[del](key);
				this[add](key, value);
			},
			configurable: true
		});
		return this;
	}

	/**
	 * delete element from aggregation
	 * @param {String} key - key of aggregation member to delete
	 * @returns {Object} this
	 * @example
	 * import Aggregation from 'lazy-aggregator';
	 * import {del} from 'lazy-aggregator';
	 * const fn = (a) => a * 2;
	 * const aggregation = new Aggregation({newEl: 3}, fn);
	 * aggregation[del]('newEl');
	 * aggregation.newEl; // undefined
	 */
	[del](key) {
		delete this[key];
		delete this[instances][key];
		return this;
	}

	/**
	 * npm install --save lazy-aggregator
	 * @name Installation
	 */
};

module.exports.add = add;
module.exports.del = del;