在 Node.js 中使用 TypeScript 异步等待

Question

我发现不可能同时做接下来的 4 件事：

1. 写入Node.js
2. 用 TypeScript 编写
3. 使用async await
4. 轻松调试

解释：

我有一个用 TypeScript 编写的 Node.js 项目，我想在其中使用 async await。

现在的问题是，如果我转译为 ES6，import 关键字会产生“意外的令牌导入”错误，如下所述：，而如果我转译为 ES5，async await 转变成不可读的代码：

这个：

///<reference path="../typings/modules/bluebird/index.d.ts" />
///<reference path="../typings/modules/mongodb/index.d.ts" />

import * as Promise from 'bluebird';
import { MongoClient, Db } from 'mongodb';
import {Campaign} from "../classes/Campaign";

export async function getCampaigns(): Campaign[] {
    try{
        var db = await connect();
        var campaigns: Campaign[] =  await db.collection("campaigns").find().toArray();
        return campaigns;
    }
    catch (err){
        console.log(err);
    }
}

async function connect(): Promise<Db> {
    return await MongoClient.connect("mongodb://localhost:27017/db");
}

变成这样：

"use strict";
var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
    return new (P || (P = Promise))(function (resolve, reject) {
        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
        function rejected(value) { try { step(generator.throw(value)); } catch (e) { reject(e); } }
        function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
        step((generator = generator.apply(thisArg, _arguments)).next());
    });
};
var __generator = (this && this.__generator) || function (thisArg, body) {
    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t;
    return { next: verb(0), "throw": verb(1), "return": verb(2) };
    function verb(n) { return function (v) { return step([n, v]); }; }
    function step(op) {
        if (f) throw new TypeError("Generator is already executing.");
        while (_) try {
            if (f = 1, y && (t = y[op[0] & 2 ? "return" : op[0] ? "throw" : "next"]) && !(t = t.call(y, op[1])).done) return t;
            if (y = 0, t) op = [0, t.value];
            switch (op[0]) {
                case 0: case 1: t = op; break;
                case 4: _.label++; return { value: op[1], done: false };
                case 5: _.label++; y = op[1]; op = [0]; continue;
                case 7: op = _.ops.pop(); _.trys.pop(); continue;
                default:
                    if (!(t = _.trys, t = t.length > 0 && t[t.length - 1]) && (op[0] === 6 || op[0] === 2)) { _ = 0; continue; }
                    if (op[0] === 3 && (!t || (op[1] > t[0] && op[1] < t[3]))) { _.label = op[1]; break; }
                    if (op[0] === 6 && _.label < t[1]) { _.label = t[1]; t = op; break; }
                    if (t && _.label < t[2]) { _.label = t[2]; _.ops.push(op); break; }
                    if (t[2]) _.ops.pop();
                    _.trys.pop(); continue;
            }
            op = body.call(thisArg, _);
        } catch (e) { op = [6, e]; y = 0; } finally { f = t = 0; }
        if (op[0] & 5) throw op[1]; return { value: op[0] ? op[1] : void 0, done: true };
    }
};

    ///<reference path="../typings/modules/bluebird/index.d.ts" />
    ///<reference path="../typings/modules/mongodb/index.d.ts" />
    var Promise = require("bluebird");
    var mongodb_1 = require("mongodb");
    function getCampaigns() {
        return __awaiter(this, void 0, void 0, function () {
            var db, campaigns, err_1;
            return __generator(this, function (_a) {
                switch (_a.label) {
                    case 0:
                        _a.trys.push([0, 3, , 4]);
                        return [4 /*yield*/, connect()];
                    case 1:
                        db = _a.sent();
                        return [4 /*yield*/, db.collection("campaigns").find().toArray()];
                    case 2:
                        campaigns = _a.sent();
                        return [2 /*return*/, campaigns];
                    case 3:
                        err_1 = _a.sent();
                        console.log(err_1);
                        return [3 /*break*/, 4];
                    case 4: return [2 /*return*/];
                }
            });
        });
    }
    exports.getCampaigns = getCampaigns;
    function connect() {
        return __awaiter(this, void 0, Promise, function () {
            return __generator(this, function (_a) {
                switch (_a.label) {
                    case 0: return [4 /*yield*/, mongodb_1.MongoClient.connect("mongodb://localhost:27017/db")];
                    case 1: return [2 /*return*/, _a.sent()];
                }
            });
        });
    }

如何解决这个悖论？

Answer 1

if I transpile to ES6, the import keyword produces "unexpected token import" error

实际上有两种解决方案。选择其中一个或组合：

• 始终使用 import / require 而不是 ES6 导入
• 指定 --module commonjs

保持目标和 ES6 并享受 :)