프로미스 내부

class CustomPromise {

  constructor(executor) {

    this.executor = executor;

    this.state = 'pending';

    this.value = null;

    const resolve = (data) => {

      if (this.state === 'pending') {

        this.state = 'fulfilled';

        this.value = data;

        this.onResolve && this.onResolve(data);

      }

    };

    const reject = (error) => {

      if (this.state === 'pending') {

        this.state = 'rejected';

        this.value = error;

        this.onReject && this.onReject(error);

      }

    };

    this.executor(resolve, reject);

  }

  then(onFulfilled, onRejected) {

    if (this.state === 'fulfilled') {

      onFulfilled(this.value);

    } else if (this.state === 'rejected') {

      onRejected(this.value);

    } else {

      this.onResolve = onFulfilled;

      this.onReject = onRejected;

    }

    return this;

  }

  catch(onRejected) {

    if (this.state === 'rejected') {

      onRejected(this.value);

    } else {

      this.onReject = onRejected;

    }

    return this;

  }

}

// 사용 예제

const myPromise = new CustomPromise((resolve, reject) => {

  setTimeout(() => {

    const isSuccess = true; // 성공 여부를 가정

    if (isSuccess) {

      resolve('성공 결과');

    } else {

      reject('오류 메시지');

    }

  }, 100);

});

myPromise

  .then((result) => {

    console.log(result); // "성공 결과" 출력

  })

  .catch((error) => {

    console.error(error); // 실행되지 않음

  });

 

 

chatGPT가 알려줌.