counter.js

/**
 * Creates a simple counter that starts at 0 and is raised by 1 on each bump.
 * @return {{getCurrentValue: (function(): number), bump: (function(): number)}}
 * @example
 * const myCounter = createCounter()
 * myCounter.getCurrentValue() // 0
 * myCounter.bump() // 1
 * myCounter.bump() // 2
 * myCounter.getCurrentValue() // 2
 */
function createCounter () {
  let currentValue = 0
  return {
    /**
     * Returns current value of the counter.
     * @return {number}
     */
    getCurrentValue: () => currentValue,
    /**
     * Bumps the value of counter and returns new value.
     * @return {number}
     */
    bump: () => ++currentValue
  }
}