NodeJS Create an array of functions and execute it through async.series

Question

Starting my learning curve on NodeJS, I am trying to call a sequence of functions using async.series. Each function is a command line that is called remotely using REST.

function TestStorageDeviceBasic()
{
    scenario = [
        'cmdline1',
        'cmdline2'
    ];

    tasks = [];
    scenario.forEach(command => { tasks.push(RunCommand(sessionId,command));});
    async.series(tasks);
}

function RunCommand(sessionId, cmdLine)
{
    var options = {
        uri: `http://${domain}/api/v1/commands`,
        method: 'POST',
        json: {
            'session-id' : `${sessionId}`,
            'command-line': `${cmdLine}` 
        }
      };

      request(options, function (error, response, body) {
        if (!error && response.statusCode == 200) {
            log.debug(`\"${cmdLine}\" status code successful`)
            log.debug(body);
        }
        else
            log.error(`\"${cmdLine}\" status code failed`,error);
      });
}

I am getting a few problems even though the RunCommand function seems to be called.

(node:21008) UnhandledPromiseRejectionWarning: Error: expected a function
    at wrapAsync (C:\work\MyJavascriptProject\my_sample\node_modules\async\dist\async.js:198:50)
    at C:\work\MyJavascriptProject\my_sample\node_modules\async\dist\async.js:2952:13

Why RunCommand is not considered a function?

You are calling RunCommand and pushing the result of the function into tasks. The result of RunCommand is not a function. You might try using .bind() to make a function with the captured parameters. — Mark
– Mark, Commented Jan 4, 2020 at 18:36
Just a comment about using async third parties: better use async await (developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…) — lastboy
– lastboy, Commented Jan 4, 2020 at 19:40

Ashish Modi · Accepted Answer · 2020-01-04 22:08:58Z

There are three things you need to modify in the code

Wrap the RunCommand in a function and then push it in tasks array
Make sure you pass callback while wrapping up
Modify the RunCommand to have a callback as well so that async.series can use the output from the callbacks.

Since you are not passing callback for your RunCommand, it is only getting executed once as async.series doesn't know when to proceed ahead. The modified code would look like

function TestStorageDeviceBasic() {
  scenario = ["cmdline1", "cmdline2"];

  tasks = [];
  scenario.forEach(command => {
    tasks.push(callack => RunCommand(sessionId, command, callack));
  });
  async.series(tasks, (err, data) => {
    if (err) {
      console.error(err);
    }
    console.log(data);
  });
}

function RunCommand(sessionId, cmdLine, callack) {
  var options = {
    uri: `http://${domain}/api/v1/commands`,
    method: "POST",
    json: {
      "session-id": `${sessionId}`,
      "command-line": `${cmdLine}`
    }
  };

  request(options, function(error, response, body) {
    if (!error && response.statusCode == 200) {
      log.debug(`\"${cmdLine}\" status code successful`);
      log.debug(body);
      callack(null, body);
    } else {
      log.error(`\"${cmdLine}\" status code failed`, error);
      callack(error, null);
    }
  });
}

Hope this helps

Thx. So when doing that, i get "Error: Callback was already called" with the stack trace. This where I am stuck for the last hour.
Where exactly are you getting this error? it is working fine for me. see this - repl.it/repls/PrevailingAshamedUtilities It is not exactly same but enough to give you an idea
could it because the next line was using err instead of error? I have updated the code. Also worth checking if log.error line is not giving any error.
I had a silly error in my code such that the braces was missing and the callback was always code. Perfect, thx a lot.

JohnnyHK · Accepted Answer · 2020-01-04 18:37:38Z

1

It's because you're calling RunCommand and then pushing its return value into tasks. Instead, push a function that makes the call:

scenario.forEach(command => { 
    tasks.push(() => RunCommand(sessionId,command));
});

answered Jan 4, 2020 at 18:37

JohnnyHK

313k70 gold badges631 silver badges477 bronze badges

2 Comments

isaac.hazan Over a year ago

Actually it did solve the problem, but only the first function is being called after calling async.series(tasks)

Ashish Modi Over a year ago

@isaac.hazan - see my answer, that has explanation of why you are seeing that behavior. Hope that helps.

Collectives™ on Stack Overflow

NodeJS Create an array of functions and execute it through async.series

2 Answers 2

4 Comments

2 Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

2 Comments

Related