@barchart/common-node-js/stream/transformations/PropertyDefaultTransformation.js

Common classes, utilities, and functions for building Node.js servers

const is = require('@barchart/common-js/lang/is');

const PropertyTransformation = require('./PropertyTransformation');

module.exports = (() => {
	'use strict';

	/**
	 * If a property doesn't exist or has an undefined value, the property
	 * will be assigned a default value; otherwise, it will be left unchanged.
	 *
	 * @public
	 * @extends {PropertyTransformation}
	 * @param {String} propertyName - The name of the property to read inspect and set to a default value.
	 * @param {*} defaultValue - The value to assign to a missing or undefined property.
	 * @param {String=} description - Describes the transformation, intended for logging purposes.
	 */
	class PropertyDefaultTransformation extends PropertyTransformation {
		constructor(defaultValue, propertyName, description) {
			super(propertyName, propertyName, (description || `Property Transformation (${propertyName})`));

			this._defaultValue = defaultValue;
		}

		_canTransform(input) {
			return true;
		}

		_transformValue(value) {
			if (is.undefined(value)) {
				return this._defaultValue;
			} else {
				return value;
			}
		}

		toString() {
			return '[PropertyDefaultTransformation]';
		}
	}

	return PropertyDefaultTransformation;
})();