Feature: add `addTask` method to `Bench`

[ivyhjk]

Motivation

Currently Bench.add() internally constructs a Task instance from (name, fn, fnOpts), leaving no room to use a Task subclass.

This change extracts that logic into a new addTask(task: Task) method that accepts an already-built Task instance. This allows creating custom Task subclasses that encapsulate specific logic (before, after, or during a benchmark run) without having to modify Bench's internal flow, improving the organization, reusability, and testability of the code that consumes the library.

This enables use cases such as validation or integrity checks before running a benchmark, custom logging or metrics, specific setup/teardown logic, or conditionally skipping a task, among others.

Changes

• add() now delegates to the new addTask() method. add()'s behavior and signature remain unchanged — this is a non-breaking change.
• Adds addTask(task: Task): this, which registers the given Task and throws an Error if one with the same name already exists.

/**
 * Adds a benchmark task to the task map.
 * @param name - the task name
 * @param fn - the task function
 * @param fnOpts - the task function options
 * @returns the Bench instance
 * @throws {Error} when a task with the same name already exists
 */
add (name: string, fn: Fn, fnOpts: FnOptions = {}): this {
  return this.addTask(new Task(this, name, fn, fnOpts))
}

/**
 * Adds a benchmark task to the task map.
 * @param task - the task to be added
 * @returns the Bench instance
 * @throws {Error} when a task with the same name already exists
 */
addTask (task: Task): this {
  if (!this.#tasks.has(task.name)) {
    this.#tasks.set(task.name, task)
    this.dispatchEvent(new BenchEvent('add', task))
  } else {
    throw new Error(`Task "${task.name}" already exists`)
  }

  return this
}

Example usage

import { Bench, Task } from 'tinybench';

class MyCustomTask extends Task {
  // ...
}

const bench = new Bench(/* ... */)
bench.addTask(new MyCustomTask(/* ... */))

Compatibility

Does not break the existing public API. add() keeps its current behavior.

TODO

• Tests for addTask (duplicate name, 'add' event dispatch)
• Update README

[jerome-benoit]

Hello, I'm not very fond of exposing such a low level method to the public API.

What would be the rationale ? what would you be the exact real world use cases ?