Question

我试图将rxjs与babeljs一起使用来创建一个异步生成器函数，该函数在调用next时产生，在调用error时抛出，在complete结束时结束} 叫做。我遇到的问题是我无法从回调中获益。

我可以await承诺来处理返回/投掷要求。

async function *getData( observable ) {
    await new Promise( ( resolve, reject ) => {
        observable.subscribe( {
            next( data ) {
                yield data; // can't yield here
            },
            error( err ) {
                reject( err );
            },
            complete() {
                resolve();
            }
        } );
    } );
}

( async function example() {
    for await( const data of getData( foo ) ) {
        console.log( 'data received' );
    }
    console.log( 'done' );
}() );

这可能吗？

Answer 1

我问橡皮鸭，然后我写了下面的代码，它做了我想要的：

function defer() {
    const properties = {},
        promise = new Promise( ( resolve, reject ) => {
            Object.assign( properties, { resolve, reject } );
        } );
        return Object.assign( promise, properties );
}

async function *getData( observable ) {
    let nextData = defer();
    const sub = observable.subscribe( {
        next( data ) {
            const n = nextData;
            nextData = defer();
            n.resolve( data );
        },
        error( err ) {
            nextData.reject( err );
        },
        complete() {
            const n = nextData;
            nextData = null;
            n.resolve();
        }
    } );
    try {
        for(;;) {
            const value = await nextData;
            if( !nextData ) break;
            yield value;
        }
    } finally {
        sub.unsubscribe();
    }
}

Answer 2

我认为这个解决方案存在的问题是，observable可以在一个批次中生成多个值（不延迟）。这是我的建议：

const defer = () => new Promise (resolve =>
    setTimeout (resolve, 0));

async function* getData (observable)
{
    let values = [];
    let error = null;
    let done = false;
    observable.subscribe (
        data => values.push (data),
        err => error = err,
        () => done = true);
    for (;;)
    {
        if (values.length)
        {
            for (const value of values)
                yield value;
            values = [];
        }
        if (error)
            throw error;
        if (done)
            return;
        await defer ();
    }
}

将Observable转换为异步生成器

2 个答案: