1.resolve

2.reject

3.手写

1.resolve

//构造函数上添加 resolve 方法
Promise.resolve = function (value) {
  return new Promise((resolve, reject) => {
    if (value instanceof Promise) {
      value.then(
        (val) => {
          resolve(val)
        },
        (err) => {
          reject(err)
        }
      )
    } else {
      resolve(value)
    }
  })
}

2.reject

Promise.reject = function (value) {
  return new Promise((resolve, reject) => {
    reject(value)
  })
}