Function formatDiff

src/utils/date.ts:44–94

(diff: number, localeFunc: LocaleFunc)

 * @returns
 */
export function formatDiff(diff: number, localeFunc: LocaleFunc): string {
  /**
   * if locale is not exist, use defaultLocale.
   * if defaultLocale is not exist, use build-in `en`.
   * be sure of no error when locale is not exist.
   *
   * If `time in`, then 1
   * If `time ago`, then 0
   */
  const agoIn = diff < 0 ? 1 : 0;

  /**
   * Get absolute value of number (|diff| is non-negative) value of x
   * |diff| = diff if diff is positive
   * |diff| = -diff if diff is negative
   * |0| = 0
   */
  diff = Math.abs(diff);

  /**
   * Time in seconds
   */
  const totalSec = diff;

  /**
   * Unit of time
   */
  let idx = 0;

  for (; diff >= SEC_ARRAY[idx] && idx < SEC_ARRAY.length; idx++) {
    diff /= SEC_ARRAY[idx];
  }

  /**
   * Math.floor() is alternative of ~~
   *
   * The differences and bugs:
   * Math.floor(3.7) -> 4 but ~~3.7 -> 3
   * Math.floor(1559125440000.6) -> 1559125440000 but ~~1559125440000.6 -> 52311552
   *
   * More information about the performance of algebraic:
   * https://www.youtube.com/watch?v=65-RbBwZQdU
   */
  diff = Math.floor(diff);

  idx *= 2;

  if (diff > (idx === 0 ? 9 : 1)) idx += 1;

  return localeFunc(diff, idx, totalSec)[agoIn].replace('%s', diff.toString());
}

/**
 * calculate the diff second between date to be formatted an now date.