Javascript Promise解决了混乱

Question

private runMiddlewares(route: Route | ExceptionRoute, request: HttpRequest, response: HttpResponse): Promise<any> {
    return new Promise((resolve, reject) => {
        try {
            route.middlewares.forEach(async (middleware: IMiddleware) => {
                console.log('begin run middleware');
                await middleware.process(request, response);
                console.log('resolve run middleware');
                console.log(request.body);
            });
            console.log('resolve all runMiddlewares');
            resolve();
        } catch (e) {
            reject(e);
        }
    });
}

我写了这个函数runMiddlewares，当所有middleware.process()都已解决时，理想情况下应该解析（）。我正在使用typescript await功能，但它似乎没有工作。我期待这样的事情发生在route.middlewares.forEach(内部

• '开始运行中间件'
• 然后等待结算
• '解析运行中间件'

这继续在forEach循环中的所有中间件，当列表全部完成然后只有'解决所有runMiddlewares'应该打印，最后，private runMiddlewares( ... )应该解决。

但相反，forEach现在正在立即解决，从而阻止所有中间件甚至完成。

应如何处理？我认为await将在forEach循环中处理它，然后才会调用resolve的runMiddlewares。我在这里错过了什么？

Answer 1

您可以使用map从中间件创建一系列承诺。这一系列的承诺可以交给Promise.all，当数组的每个承诺都得到解决时，它会解决。

await Promise.all(route.middlewares.map((middleware: IMiddleware) => {
            console.log('begin run middleware');
            const promise = middleware.process(request, response);
            console.log('resolve run middleware');
            console.log(request.body);
            return promise
        });

或者更紧凑：

runMiddlewares(...) {
  return Promise.all(
    route.middlewares.map((middleware: IMiddleware) => {
      return middleware.process(request, response))
    })
  )
}

Answer 2

所以，按照建议（https://cn.eslint.org/docs/3.0.0/rules/no-await-in-loop），我写了如下

private runMiddlewares(route: Route | ExceptionRoute, request: HttpRequest, response: HttpResponse): Promise<any> {
    return new Promise(async (resolve, reject) => {
        try {
            const middlewarePromiseArry: any[] = [];
            route.middlewares.forEach((middleware: IMiddleware) => {
                console.log('begin run middleware');
                middlewarePromiseArry.push(middleware.process(request, response));
                // removed the use of await inside of forEach loop following this link: https://cn.eslint.org/docs/3.0.0/rules/no-await-in-loop
                // await middleware.process(request, response);
                // console.log('resolve run middleware');
                // console.log(request.body);
            });

            await Promise.all(middlewarePromiseArry);
            console.log('resolve all runMiddlewares');
            resolve();
        } catch (e) {
            reject(e);
        }
    });
}

我很高兴接受进一步的答案和建议/改进:)