TypeError: Chaining cycle detected for promise!

[taoeer]

测试代码

const Promise = require('./promise');

function go() {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve();
    }, 1000);
  });
}

function r() {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      reject();
    }, 2000);
  });
}

Promise.all([go(),r()]).then(v => {
  console.log('resolve', v);
}).catch(v => {
  console.log('reject', v);
});

原因可能是

/**
 * 将现有对象转为成功的Promise对象
 */
Promise.resolve = function (value) {
  let promise;
  return (promise = new Promise((resolve, reject) => {
    resolvePromise(promise, value, resolve, reject); // 参数promise永远是undefined
  }));
};

改为

Promise.resolve = function (value) {
  if (value instanceof Promise) {
    return value;
  }
  return new Promise(resolve => resolve(value));
};

[Hexa-gram]

感谢指正

[lhz960904]

 if (value instanceof Promise) {
    return value;
  }
  return new Promise(resolve => resolve(value));

原因是因为：Promise.resolve中调用resolvePromise，promise永远是undefined，当promise的结果也是undefined就会命中循环引用的判断。

function resolvePromise(promise, x, resolve, reject) {
  // 如果 promise 和 x 指向同一对象，以 TypeError 为据因拒绝执行 promise
  if ( x === promise) {
    // 命中这个逻辑！！！
    return reject(new TypeError('Chaining cycle detected for promise!'));
  }
  // 忽略无关代码
}

解决方案：

// 判断promise不空的时候校验
if ( promise && x === promise) {
  return reject(new TypeError('Chaining cycle detected for promise!'));
}

或

@taoeer 提供的

Promise.resolve = function (value) {
  if (value instanceof Promise) {
    return value;
  }
  return new Promise(resolve => resolve(value));
};