old_contents: let isArray = v => Object.prototype.toString.call(v) === '[object Array]';
  let isString = v => typeof v === 'string';
  let isFunction = v => typeof v === 'function';
  
  export { isArray, isString, isFunction };
  
new_contents: /**
   * Checks if the given value is an array.
   *
   * @param {*} value
   * @returns {boolean}
   */
  export function isArray(value) {
      return Object.prototype.toString.call(value) === '[object Array]';
  }
  
  /**
   * Checks if the given value is a string.
   *
   * @param {*} value
   * @returns {boolean}
   */
  export function isString(value) {
      return typeof value === 'string';
  }
  
  /**
   * Checks if the given value is a function.
   *
   * @param {*} value
   * @returns {boolean}
   */
  export function isFunction(value) {
      return typeof value === 'function';
  }
  
subject: Rewrite util.js