n/handle-callback-err

A Node.js callback gets the error as its first argument. If the function never looks at it, a failure goes unnoticed, and the code carries on with a result that's undefined.

The rule reports a function with a first parameter named err that's never used in its body. Any use counts. The rule doesn't check what you do with the error.

Configure#

Off by default. To turn it on:

[lint.rules]
"n/handle-callback-err" = "error" # or "warn"

Examples#

Reported:

fs.readFile("config.json", (err, data) => {
  start(JSON.parse(data));
});

Not reported:

fs.readFile("config.json", (err, data) => {
  if (err) {
    throw err;
  }
  start(JSON.parse(data));
});

Options#

The option is the name of the error parameter. The default is "err". If it starts with ^, it's treated as a regular expression.

[lint.rules]
"n/handle-callback-err" = ["error", "^(err|error)$"]

server.close(function (error) {
  console.log("closed");
});

socket.end(function (err) {
  console.log("ended");
});

A plain name replaces err, so err is no longer checked:

socket.end(function (err) {
  console.log("ended");
});