JavaScript 链式 Promises 意外的解析顺序

Question

我对这两个不同函数的执行感到困惑，我希望它们以相同的顺序解析，但显然，它们没有。

    // given this function:
let promiseDelay = () => new Promise( resolve => { setTimeout( () => { console.log( '========' ); resolve(); }, 1000 ) } );

// execution 1:
const promise1 = Promise.resolve( {} ).then( promiseDelay ).then( () => console.log( 'Job done!' ) ).then( promiseDelay ).then( () => console.log( 'Job done!' ) );

// given this function:
const promiseDelay = () => new Promise( resolve => { setTimeout( () => { console.log( '========' ); resolve(); }, 1000 ) } );

// execution 2:
const promise = Promise.resolve( {} );
promise.then( promiseDelay );
promise.then( () => console.log( 'Job done!' ) );
promise.then( promiseDelay );
promise.then( () => console.log( 'Job done!' ) );

Answer 1

您实际上并没有在这里链接 Promise，您只是将多个函数附加到 Promise，所有函数都同时执行。

要链式 Promise，请依次编写下一个 .then():

// given this function:
promiseDelay = () => new Promise( resolve => { setTimeout( () => { console.log( '========' ); resolve(); }, 1000 ) } );

// execution 1:
promise = Promise.resolve( {} ).then( promiseDelay ).then( () => console.log( 'Job done!' ) ).then( promiseDelay ).then( () => console.log( 'Job done!' ) );

// execution 2:
promise = Promise.resolve( {} );
promise.then( promiseDelay )
    .then( () => console.log( 'Job done!' ) )
    .then( promiseDelay )
    .then( () => console.log( 'Job done!' ) );