throttle.js

import debounce from './debounce';
import isObject from './isObject';

/**
 * Creates a throttled function that only invokes `func` at most once per
 * every `wait` milliseconds (or once per browser frame). The throttled function
 * comes with a `cancel` method to cancel delayed `func` invocations and a
 * `flush` method to immediately invoke them. Provide `options` to indicate
 * whether `func` should be invoked on the leading and/or trailing edge of the
 * `wait` timeout. The `func` is invoked with the last arguments provided to the
 * throttled function. Subsequent calls to the throttled function return the
 * result of the last `func` invocation.
 *
 * **Note:** If `leading` and `trailing` options are `true`, `func` is
 * invoked on the trailing edge of the timeout only if the throttled function
 * is invoked more than once during the `wait` timeout.
 *
 * If `wait` is `0` and `leading` is `false`, `func` invocation is deferred
 * until the next tick, similar to `setTimeout` with a timeout of `0`.
 *
 * If `wait` is omitted in an environment with `requestAnimationFrame`, `func`
 * invocation will be deferred until the next frame is drawn (typically about
 * 16ms).
 *
 * See [David Corbacho's article](https://css-tricks.com/debouncing-throttling-explained-examples/)
 * for details over the differences between `throttle` and `debounce`.
 *
 * @param {Function} func The function to throttle.
 * @param {number} [wait=0]
 *  The number of milliseconds to throttle invocations to; if omitted,
 *  `requestAnimationFrame` is used (if available).
 * @param {Object} [options={}] The options object.
 * @param {boolean} [options.leading=true]
 *  Specify invoking on the leading edge of the timeout.
 * @param {boolean} [options.trailing=true]
 *  Specify invoking on the trailing edge of the timeout.
 * @returns {Function} Returns the new throttled function.
 * @example
 *
 * // Avoid excessively updating the position while scrolling.
 * jQuery(window).on('scroll', throttle(updatePosition, 100))
 *
 * // Invoke `renewToken` when the click event is fired, but not more than once every 5 minutes.
 * const throttled = throttle(renewToken, 300000, { 'trailing': false })
 * jQuery(element).on('click', throttled)
 *
 * // Cancel the trailing throttled invocation.
 * jQuery(window).on('popstate', throttled.cancel)
 */
function throttle(func, wait, options) {
  let leading = true;
  let trailing = true;

  if (typeof func !== 'function') {
    throw new TypeError('Expected a function');
  }
  if (isObject(options)) {
    leading = 'leading' in options ? Boolean(options.leading) : leading;
    trailing = 'trailing' in options ? Boolean(options.trailing) : trailing;
  }

  return debounce(func, wait, {
    leading,
    trailing,
    maxWait: wait,
  });
}

export default throttle;