Implementation of Elm's classList function. Allows to conditionally apply classes according to the current state

classList.js

/**
 * @fileOverview Implementation of Elm's classList function.
 *               Allows to conditionally apply classes according to the current state
 *               [source]{@link https://package.elm-lang.org/packages/evancz/elm-html/3.0.0/Html-Attributes#classList}
 *
 * @param {string[ [string, bool] ]} rules - An array of rules. Every rule has 2 elements:
 *                                          element.0: string, the class you want to apply
 *                                          element.1: bool, whether or not to apply the class
 * @return {string} - The interpolated string of classes
 *
 * @example
 * // returns 'class1'
 * classList([ ['class1', true], ['class2', false] ])
 *
 * @example
 * // returns ''
 * classList([ ['class1', false], ['class2', false] ])
 *
 * @example
 * // return 'active' or '' according to the value in this.state.isActive
 * classList([ ['active', this.state.isActive] ])
 */

export default function classList(rules) {
  return rules.filter(rule => rule[1])
    .map(rule => rule[0])
    .join(' ')
}