@es-toolkit/es-toolkit@1.17.0

Built and signed on GitHub Actions

Built and signed on GitHub Actions

123456789101112131415161718192021222324252627282930313233343536373839404142
/**
 * Creates a function that only executes starting from the `n`-th call.
 * The provided function will be invoked starting from the `n`-th call.
 *
 * This is particularly useful for scenarios involving events or asynchronous operations
 * where an action should occur only after a certain number of invocations.
 *
 * @template F - The type of the function to be invoked.
 * @param {number} n - The number of calls required for `func` to execute.
 * @param {F} func - The function to be invoked.
 * @returns {F} - A new function that:
 * - Tracks the number of calls.
 * - Invokes `func` starting from the `n`-th call.
 * - Returns `undefined` if fewer than `n` calls have been made.
 * @throws {Error} - Throws an error if `n` is negative.
 * @example
 *
 * const afterFn = after(3, () => {
 *  console.log("called")
 * });
 *
 * // Will not log anything.
 * afterFn()
 * // Will not log anything.
 * afterFn()
 * // Will log 'called'.
 * afterFn()
 */

export const after = <F extends (...args: any[]) => any>(n: number, func: F): F => {
  if (!Number.isInteger(n) || n < 0) {
    throw new Error(`n must be a non-negative integer.`);
  }

  let counter = 0;
  return ((...args: Parameters<F>) => {
    if (++counter >= n) {
      return func(...args);
    }
    return undefined;
  }) as F;
};