Why error is passed as the first argument to the callback in nodeJs?

Question

In nodeJs callback pattern, an error is encountered during execution. this error is passed as the first argument to the callback! What are the advantages of this pattern?

for example:

fs.readFile(filePath, function(err, data) { }

Why err is the first argument in this pattern?

That's the way it is you can define some function which accepts callback with data as first argument there isn't any hard rule that you can't use that but it's just a community standard so that developers get used to it. — Black Mamba, Apr 22 '19 at 18:57
surely, but there must be other rational reasons... @‌Black Mamba — mojtaba ramezani, Apr 22 '19 at 19:05

score 2 · Answer 1 · answered Apr 22 '19 at 19:08

More often you are more interested if an error occurred, than to the actual data returned, so you will write this more:

function(err) {}

if the error was not the first argument, you always have to use a variable for the data you don't care about.

function(_, err) {}

More over, the error first approach, will 'force' you, or at least remind you to check if there is an error, if you already have to name it in your callback

Why error is passed as the first argument to the callback in nodeJs?

1 Answers1