Asynchronous handlers

All of the examples shown so far in this chapter assume that handlers are synchronous. In a real application, many handlers will need to be asynchronous.

Nest.js provides a number of approaches to write asynchronous request handlers.

Async/await

Nest.js has support for async request handler functions.

In our example application, the entriesService.findAll() function actually returns a Promise<Entry[]>. Using async and await, this function could be written as follows.

import { Controller, Get } from '@nestjs/common';

@Controller('entries')
export class EntryController {
    @Get()
    async index(): Promise<Entry[]> {
        const entries: Entry[] = await this.entryService.findAll();
        return entries;
    }

Async functions have to return promises, but using the async/await pattern in modern JavaScript, the handler function can appear to be synchronous. Next, we’ll resolve the returned promise and generate the response...