How to stop execution of a node.js script?

Question

Say I've got this script:

var thisIsTrue = false;

exports.test = function(request,response){

    if(thisIsTrue){
        response.send('All is good!');
    }else{
        response.send('ERROR! ERROR!');
        // Stop script execution here.
    }

    console.log('I do not want this to happen if there is an error.');

}

And as you can see, I'd like to stop the script from executing any downstream functions if there's an error.

I've managed to achieve this by adding return; after the error response is sent:

var thisIsTrue = false;

exports.test = function(request,response){

    if(thisIsTrue){
        response.send('All is good!');
    }else{
        response.send('ERROR! ERROR!');
        return;
    }

    console.log('I do not want this to happen if there is an error.');

}

But is that the 'correct' way to do things?

Alternatives

I've also seen examples that use process.exit(); and process.exit(1);, but that gives me a 502 Bad Gateway error (I assume because it kills node?).

And callback();, which just gave me an 'undefined' error.

What is the 'correct' way to stop a node.js script at any given point and prevent any downstream functions from executing?

Answer 1

Using a return is the correct way to stop a function executing. You are correct in that process.exit() would kill the whole node process, rather than just stopping that individual function. Even if you are using a callback function, you'd want to return it to stop the function execution.

ASIDE: The standard callback is a function where the first argument is an error, or null if there was no error, so if you were using a callback the above would look like:

var thisIsTrue = false;

exports.test = function(request, response, cb){

    if (thisIsTrue) {
        response.send('All is good!');
        cb(null, response)
    } else {
        response.send('ERROR! ERROR!');
        return cb("THIS ISN'T TRUE!");
    }

    console.log('I do not want this to happen. If there is an error.');

}

Answer 2

You can use process.exit() to immediately forced terminate a nodejs program.

You can also pass relevant exit code to indicate the reason.

• process.exit() //default exit code is 0, which means *success*

• process.exit(1) //Uncaught Fatal Exception: There was an uncaught exception, and it was not handled by a domain or an 'uncaughtException' event handler

• process.exit(5) //Fatal Error: There was a fatal unrecoverable error in V8. Typically a message will be printed to stderr with the prefix FATAL ERROR

---

More on exit codes

Answer 3

You should use return, which will help you respond to what happened. Here's a bit cleaner version, basically first validate whatever you want to validate, rather than encapsulating everything in if{}else{} statements

exports.test = function(request, response, cb){

    if (!thisIsTrue) {
        response.send('ERROR! ERROR!');
        return cb("THIS ISN'T TRUE!");
    }

    response.send('All is good!');
    cb(null, response)

    console.log('I do not want this to happen. If there is an error.');

}

Another way would be to use throw

exports.test = function(request, response, cb){

    if (!thisIsTrue) {
        response.send('ERROR! ERROR!');
        cb("THIS ISN'T TRUE!");
        throw 'This isn\'t true, perhaps it should';
    }

    response.send('All is good!');
    cb(null, response)

    console.log('I do not want this to happen. If there is an error.');

}

Finally, examples that would stop entire app from further execution:

a) Throw an error, which will also help you debug the app (wouldn't completely stop the app, if the test() function was wrapper in try{}catch(e){}):

throw new Error('Something went wrong')

b) Stop script execution (works with Node.js):

process.exit()