Promise

Constructor

Promise

• 描述：封装一个 Promise
• 语法：new Promise(executor)
• 参数
  • executor(resolve?, reject?)：构造函数
    • resolve：兑现一个 promise
    • reject：拒绝一个 promise

let p = new Promise((resolve, reject) => {
    resolve(1)
}) // fulfilled 1

Static Methods

all

• 语法：Promise.all(iterable)
• 返回值
  • fulfilled：所有 promise fulfilled
  • rejected：任意 promise rejected

Promise.all([Promise.resolve(1), Promise.resolve(2)]) // fulfilled [1, 2]
Promise.all([Promise.resolve(1), Promise.reject(2)]) // rejected 2

any

• 语法：Promise.any(iterable)
• 返回值
  • fulfilled：任意 promise fulfilled
  • rejected：所有 promise rejected

Promise.any([Promise.resolve(1), Promise.resolve(2)]) // fulfilled 1
Promise.any([Promise.reject(1), Promise.reject(2)]) // rejected AggregateError

race

• 语法：Promise.race(iterable)
• 返回值
  • fulfilled：任意 promise fulfilled
  • rejected：任意 promise rejected

Promise.race([Promise.resolve(1), Promise.reject(2)]) // fulfilled 1
Promise.race([Promise.reject(1), Promise.resolve(2)]) // rejected 1

allSettled

• 语法：Promise.allSettled(iterable)
• 返回值
  • fulfilled：所有 promise fulfilled or rejected

Promise.allSettled([Promise.resolve(1), Promise.reject(2)]) // fulfilled [1, 2]

resolve

• 语法：Promise.resolve(value)
• 返回值：fulfilled

Promise.resolve(1) // fulfilled 1

reject

• 语法：Promise.reject(value)
• 返回值：rejected

Promise.reject(1) // rejected 1

withResolvers

• 语法：Promise.withResolvers()
• 返回值：{ promise, resolve, reject }

let { promise, resolve, reject } = Promise.withResolvers()
resolve(1)
promise // resolved 1

Instance Methods

then

• 描述：为 promise 注册 fulfilled 和 rejected 时的回调
• 语法：then(onFulfilled?, onRejected?)
• 参数
  • onFulfilled = x => x：fulfilled 时的回调
  • onRejected = x => { throw x }：rejected 时的回调

Promise.resolve(1).then(
    val => { console.log('ok ' + val) },
    val => { console.log('error ' + val) }
) // ok 1

catch

• 描述：为 promise 注册 rejected 时的回调
• 语法：catch(onRejected?)
• 参数
  • onRejected = x => { throw x }：rejected 时的回调

Promise.reject(1).catch(
    val => { console.log('error ' + val) }
) // error 1

finally

• 描述：为 promise 注册 settled 时的回调
• 语法：finally(onFinally?)
• 参数
  • onFinally = x => x：settled 时的回调

Promise.resolve(1).finally(
    () => { console.log('finally') }
) // finally
 
Promise.reject(1).finally(
    () => { console.log('finally') }
) // finally