Treating error in callback function

Question

I’m trying to fix a mistake in the following code:

const fs = require('fs')

fs.readFile('dados/arqui2vo.json', (err, data) => {

    if (err) throw new Error(`Can't find the file`)

When I run the code, this message appears on the console:

c:\Users\<User>\Documents\Node\readFile.js:5
if (err) throw new Error(`Can't find the file`)
         ^

Error: Can't find the file
    at ReadFileContext.fs.readFile [as callback] (c:\Users\<User>\Documents\Node\readFile.js:5:20)
    at FSReqWrap.readFileAfterOpen [as oncomplete] (fs.js:237:13)

How can I show the error message I created? This is the message I’d like to appear on my console:

Error: Can't find the file

Answer 1

The error shown in the terminal is being created on the following line:

if (err) throw new Error('Can\'t find the file');

Note that you are not treating the error in the most usual way since you are creating a new error (throw new Error), which will probably not be dealt with at another time, which will issue an error in the terminal, as you reported in your question.

So instead of creating a new error within the callback, seek only to display information on console, to let you know that an error has occurred. Something like this:

if (err) {
  console.error('Ocorreu um erro ao tentar ler o arquivo.');
}

That way, you’re performing the due process of error, and the Node.js process will continue to run normally, as the error has been properly handled.

And if you want to quit the application when an error occurs, just use the process.exit:

if (err) {
  console.error('<sua mensagem de erro aqui>');
  process.exit(1);
}

In the code above, we pass 1 as the first argument for the method process.exit, to indicate that an error caused the termination of the process.

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^{Note that for larger applications that will be used in a production environment, display only a warning message by console may not be enough. Search in depth for how to treat a production error if you want to know more.}