My NodeJS application is using spring cloud server for configurations and I am loading this at the application startup. I am using the below function to load config but I can see the promise status is pending and seems to be the call is still async. How can I make it as a sync call to wait until the configurations are loaded. Thanks in advance!
async function fetchConfig(){
await client.getConfig().then(conf => {
console.log(conf);
}).catch(console.error);
}
async/await is a way to replace promise based callback, but you use them at same time, you can change it to:
async function fetchConfig(){
try {
const conf = await client.getConfig();
console.log(conf);
} catch (ex) {
console.error(ex);
}
}
Related
I'm trying to test an ExpressJS (4.17.8) and NodeJS (16.3) powered server (app) with tap, and later with supertest. First I'm testing the instantiation of the server, and later its routes.
For this, my app is wrapped in a Connector Class that:
has an ExpressJS server (app)
connects to an external system
registers endpoints
has a method startup that calls app.listen
So I have a test file like this:
import test, { Test } from "tape-promise/tape";
test("connects to X", async (t: Test) => {
connector = new Connector();
await connector.ConnectToExternalSystem(); // connects to external system
await connector.registerEndpoints(); // e.g., sets to the Express app: app[get](/endpoint)...
await connector.listen(); // gets stuck?
t.ok(connector);
t.end();
My problem is that for every test I perform, tap seems to get stuck (happens with Jest as well) in connector.listen() - leading for the test to timeout.
My project and tests are written in Typescript 4.3.5. I am using the following npm script to run the tests:
"test": "tap --ts --jobs=1 --node-arg=--max-old-space-size=4096 --timeout=15 --branches=45 --functions=70 --lines=75 --statements=75 \"src/test/{unit,integration}/\"",
Is there anything I'm doing wrong? Appreciate your advice on this.
Thanks.
Depends on what the implementation of Connector really looks like. Assuming that the .listen() method of it calls express' listen under the hood the issue might be that you are not handling the success callback or that it's not wired up properly to the returned promise via the resolve callback of the promise.
So something like this could work (rough pseudo code, not tested):
class Connector {
listen(): Promise<void> {
return new Promise((resolve, reject) => {
this.expressApp.listen((err: Error) => {
if (err) {
reject(err);
} else {
resolve();
}
});
});
}
}
What the above does is ensures that the returned promise resolves once the callback has been invoked (or rejects if the callback was passed in an error which is the standard NodeJS error handling style)
I am trying to use async await to execute an http request before executing some other code.
More precisely, I would like to drop a collection in my mongodb database, before executing some others tasks. Here's what I did:
app.component.ts:
async deleteRiskRatingData2() {
await this.saveInformationService
.deleteRiskRatingInformation()
.subscribe((data: string) => {
console.log('Deleting risk Rating');
console.log(this.riskRatingTable);
});
console.log('TASKS TO BE EXECUTED AFTER DROPIING COLLECTION');
}
save-information.service.ts
deleteRiskRatingInformation() {
console.log('INIDE deleteRiskRatingInformation INSIDE SAVE-INFORMATION.SERVICE');
return this.http.get(`${this.uri}/dropRiskRatingCollection`);
}
In the backend:
server.js
router.route('/dropRiskRatingCollection').get((req, res) => {
RiskRating.remove({},(err) => {
if (err)
console.log(err);
else
res.json("Risk Rating Collection has been dropped!");
});
});
And this is what happens:
I though my implementation of Async/Await should allow me to execute the:
console.log('TASKS TO BE EXECUTED AFTER DROPPING COLLECTION');
After the dropping of the collection request has been executed. But that didn't happen as you see. And I really don't understand why.
Any idea why is this happening? Is my logic flawed somewhere? And how can I achieve my goal?
Thank you!
async-await work only with Promises. You're try them with Observables. That won't work. Observables have an API that let's you convert them into Promises though. You can call a toPromise method on them in order to do that.
Try this:
async deleteRiskRatingData2() {
const data = await this.saveInformationService.deleteRiskRatingInformation().toPromise();
console.log('Deleting risk Rating');
console.log(this.riskRatingTable);
console.log('TASKS TO BE EXECUTED AFTER DROPIING COLLECTION');
}
NOTE: It's fine if you're trying this just for the sake of testing it. But I think you should not really switch back to promises just to use async-await, to make your code look synchronous.
I have many async functions in my system, so I need to go "async all the way down", which is to the point where the http.Server and express.Application app are created.
(This is unavoidable in an async system - there will be many async routines which are needed in constructors, which cannot be done, and so we need to use async factory functions instead, which lead to async creep all the way down to the entry point.)
But I'm not sure of the Node/TypeScript syntax to use to bootstrap the app.
My main entry point is System.ts:
class default export System {
public constructor() {
// init Express.Application
// init http.Server
// init other parts of the system
}
public async start(): Promise<void> {
// start the system asynchronously
// start listening with http.Server
}
}
Then I have a bootstrapping module Main.ts:
import System from "./System"
const system = new System();
export default ???; // PROBLEM IS HERE
Which should be run:
node ./dist/Main.js
But I'm not sure what to use in the export line. I tried all these:
export default await system.start(); // doesn't compile (obviously)
export default system.start(); // doesn't seem right
export default system.start().then(); // this works *maybe*
The last line works based on a smoke test - but I'm not sure if that's the way to do it, and whether there's something down the line that may fail.
What is the canonical way to start an asynchronous node app?
UPDATE
Based on #JacobGillespie's answer, the Main.ts bootstrapping module is now:
import System from "./System"
new System().start().then();
//new System().start().catch(e => console.error(e)); // alternative
In my case, System.ts has handlers for errors and unhandled promises, and does logging (otherwise use the "alternative" line). So the bootstrapping module just bootstraps the system.
async / await here are operating on promises, so you essentially want to "start" the promise by calling .then or .catch.
My go-to snippet for this is creating an async run or main function, then attaching error handling to the process, something like this:
async function run() {
// run the app, you can await stuff in here
}
run().catch(err => {
console.error(err.stack)
process.exit(1)
})
In your case that would look like (Main.ts):
import System from "./System"
async function run() {
const system = new System()
await system.start()
}
run().catch(err => {
console.error(err.stack)
process.exit(1)
})
You don't need to export anything since this module file isn't being imported anywhere else (it's the entry file).
You can just call system.then() or system.catch(), but personally I like the async function run() pattern since you may need to coordinate more than one async thing in the future and this makes the code more explicit.
system.start().then() => {
value => export default value
}
In my opinion, a better way would be:
System.ts:
function System():Promise<string>{
//setup express and the server
return new Promise((res,rej) => {
//the server var is just the http server instance
server.listen(8000,() => resolve("server created"));
});
}
export {System}
And then in Main.ts:
import {System} from "yourpath"
And then:
System().then(() => {
//code runs when server is created
}).catch(err => console.error(err));
I'm using the function driver.wait(until.elementLocated()) below, written with node.js, as an explicit wait on my Selenium tests to ensure that the pages in my test load properly. When I run the tests from my local CLI they work perfectly, headlessly and with GUI.
const loadMyPage = {
loadThePage: async function(driver) {
try {
await driver.wait(
until.elementLocated(
By.css("div.radio-select span:nth-child(7)")
),
20000
);
} catch (e) {
console.trace(loadMyPage.loadThePage);
throw e;
}
}
However, when I run the tests in Jenkins headlessly I receive the following error every time I use the function elementLocated().
TypeError: Wait condition must be a promise-like object, function, or a Condition object[0m[90m
at Driver.wait (node_modules/selenium-webdriver/lib/webdriver.js:928:13)
at Object.loadMyPage (foobar-tests/page.js:35:20)
at Context.<anonymous> (foobar-tests/foobar.test.js:32:30)
at <anonymous>
Is there anything specific that could cause this error in Jenkins? I have managed to narrow it down to this specific function, elementLocated().
I was able to find a workaround for my issue, however it appears that there is a larger issue at play with selenium. More information on the core issue can be found at https://github.com/SeleniumHQ/selenium/issues/5560.
I updated my explicit wait by passing an additional async function, and this cleared up the problem entirely in Jenkins. Example is below.
loadMyPage: async () => {
//The second async is necessary to run explicit wait functions like the one below.
//This issue is specific to selenium, more information can be found at https://github.com/SeleniumHQ/selenium/issues/5560.
loadThePage: async () {
try {
async driver =>
await driver.wait(
until.elementLocated(
By.css("div.radio-select span:nth-child(7)")
),
10000
);
} catch (e) {
console.trace(loadMyPage.loadThePage);
throw e;
}
}
In my Cordova project, I have a hook which does RequireJS optimization (r.js) on after_prepare. That optimization is inherently asynchronous, so my hook code returns before all optimization is fully finished.
For example, this causes issues when running cordova run browser: On the first page load, optimization has not finished yet and the site looks broken.
Is there a way to make the Cordovoa build process to block until a certain hook fires a callback? Or can the optimizer be run in a blocking/sync way?
An alternative I could think of is using a different process for optimization and busy-wait in the main for it to finish, but that looks like an overkill and bad practice to me.
You can use the built-in promise module to block Cordova from proceeding until the hook has resolved.
Something along these lines:
#!/usr/bin/env node
var deferral;
function doSomethingAsync(){
somethingAync
.success(function(){
deferral.resolve();
})
.fail(function(err){
deferral.reject(err);
});
}
module.exports = function(ctx) {
deferral = ctx.requireCordovaModule('q').defer();
doSomethingAsync();
return deferral.promise;
};
You don't need to call context, you can simply return a Promise from within the module.exports function
module.exports = context => {
return new Promise(resolve => {
setTimeout(() => resolve(), 1000);
});
};
I tested and it works. The problem arises because in Cordova versions => 9 you cannot use context.requireCordovaModule('q')
If you don't want to use Promise, just do
module.exports = context => {
var deferral = require('q').defer();
doSomethingAsync(() => {
deferral.resolve();
});
return deferral.promise;
};