Alon Alon - 1 month ago 6
Javascript Question

Using TypeScript async await in Node.js

I've found it impossible to do all the next 4 things togother:


  1. Writing in Node.js

  2. Writing in TypeScript

  3. Using
    async await

  4. Debugging easily



Explanation:

I have a Node.js project written in TypeScript in which I'm tring to use
async await
.

Now the problem is that if I transpile to ES6, the import keyword produces "unexpected token import" error as disscused here: ES6 import and export are not supported in Node.js, while if I transpile to ES5, the
async await
turn into unreadable code:

This:

///<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");
}


becomes this:

"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()];
}
});
});
}


How can I solve this paradox?

Answer

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

There are actually two solutions. Pick either or combination:

  • Always use import / require instead of ES6 imports
  • Specify --module commonjs

Keep the target and ES6 and enjoy :)

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