Run async code from command line, node js

Question

I have a function that generates some test data and inserts it to a mongodb:

'use strict';
const CvFaker = require('./cv-faker');
const mongoose = require('mongoose');
require('../models/cv_model.js');

module.exports.init = function(){
  var cvfaker = new CvFaker();
  cvfaker.genCvs(100);

  mongoose.model('cv').create(cvfaker.cvs, (err, createdCvs) => {
    if(err){
      console.log('something went wrong');
    }

  })
};

I want to execute this code from the command line:

node -e 'require("./create-mock-db").init()'

The function executes, but it does not wait for the function to complete since it is async. How do I make it wait for the function to complete?

This is not working either:

module.exports.init = function(cb){ ...
..
cb();

node -e 'require("./create-mock-db").init(function(){})'

In Javascript, functions do not wait for async operations to be done. They just don't. Usually, you use a completion callback to continue your logic there after the async operation is done. If you describe what actual problem you're trying to solve by waiting, we can probably help you with alternatives. — jfriend00
– jfriend00, Commented Aug 3, 2016 at 15:13
Yes, but how do I add the callback when I'm executing from commandline? — Joe
– Joe, Commented Aug 3, 2016 at 15:19
Why not create your own script that loads this module and uses a completion callback as intended. It's hard to write complicated code one line at a time on the console. But, you could pass a callback to .init() that gets called when the async operation is done. — jfriend00
– jfriend00, Commented Aug 3, 2016 at 15:20
Since this code should not be in production, only in dev-mode, I don't want to expose it, hence I want to execute it from the command-line. I don't find any way to do so if you have async code. — Joe
– Joe, Commented Aug 3, 2016 at 15:35
It's nuts to do this on the console! But, you can type a function into the console previously so its symbol is defined. Then, pass that symbol as an argument to .init() as a callback function. — jfriend00
– jfriend00, Commented Aug 3, 2016 at 15:38

Jake Holzinger · Accepted Answer · 2020-02-10 21:33:32Z

The node process will not exit until the event queue is empty. The event loop uses the event queue to make asynchronous execution possible.

It's pretty simple to verify that this is not an issue with executing asynchronous code.

node -e "setTimeout(() => console.log('done'), 5000)"

This example takes 5 seconds to run, as you would expect.

The problem with your code is the fact that you never establish a connection with the database. The model.create method doesn't do anything until there is a connection, therefor nothing ever gets queued and the process is free to exit.

This means your code needs to change to do two things:

Connect to the database so that the model.create method can execute.
Disconnect from the database when model.create is complete so the process is free to exit.

kaiser · Accepted Answer · 2020-02-10 20:47:24Z

As this answer might come up for more people…

// test.js
const request = require('request');
const rp = require('request-promise');

const demo = module.exports.demo = async function() {
  try {
    const res = await rp.post( {
      uri: 'https://httpbin.org/anything',
      body: { hi: 'there', },
    }, function (error, response, body) {
      return error ? error : body;
    } )
    console.log( res )
    return res;
  }
  catch ( e ) {
    console.error( e );
  }
};

Call it like this:

$ node -e 'require("./test").demo()'

Sidenote:

it does not wait for the function to complete since it is async

It's not async. You might call asynchronous functions, but you are not treating them as such and not awaiting any result.

Raphi OKG · Accepted Answer · 2022-05-11 00:17:11Z

0

To add to Kaiser's answer, if you are on Windows using cmd, the single/double quotes are important. Put the double quotes on the outside, i.e.

node -e "require('./test').demo()"

answered May 11, 2022 at 0:17

Raphi OKG

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