effect返回runner单测实现示例详解

it('runner', function () {
  // effect(fn) -> return runner -> runner() == fn() -> return
  let foo = 10;
  const runner = effect(() => {
    foo++;
    return 'foo';
  });
  expect(foo).toBe(11);
  const r = runner();
  expect(foo).toBe(12);
  expect(r).toBe('foo');
});

class ReactiveEffect {
  private _fn: any;
  constructor(fn) {
    this._fn = fn;
  }
  run() {
    activeEffect = this;
    // + 返回fn的返回值
    return this._fn();
  }
}
export function effect(fn) {
  const _effect = new ReactiveEffect(fn);
  _effect.run();
  // + 涉及到run()中this指向的问题，所以需要bind处理一下。
  return _effect.run.bind(_effect);
}