Promise(二)

resolve参数

1. 普通参数传递

   let promiseFn = ()=>{
     return new Promise((resolve,reject)=>{
       resolve( { name: 'nano' } )
     })
   }
   promiseFn().then( res => { console.log(res) } ) --> { name: 'nano' }

   注意: 一次只能传递一个参数

2. 传递promise

   let promiseFn=() => {
   return new Promise((resolve,reject) => {
       resolve(new Promise((resolve,reject) => {
           resolve(111)
           reject(222)
       }))
     })
   }
   /* 如果是fulfilled状态 */
   promiseFn().then(res => {console.log(res)})  --> 111
   
   * 如果是rejected状态 */
   promiseFn().catch(err => {console.log(err)})  --> 222
   
   /* 如果是pending状态则.then或者.catch什么都不打印 */

   值得注意: 如果resolve传递的是promise函数,那么当前promise函数状态由resolve中传递的promise函数决定

3. 传入一个对象并且对象中有then方法,那么当前promise函数的状态由对象中的then方法决定,并且该then函数自动创建resolve,reject两个参数

    let promiseFn=() => {
        return new Promise((resolve,reject) => {
          resolve({
            /* thenable */
            then(resolve,reject) {
              resolve(22)
              reject(33)
            }
          })
      })
   }
   promiseFn().then(res => {console.log(res)}) --> 22
   promiseFn().catch(res => {console.log(res)}) --> 33