Why does node prefer an error callback?

Question

Node programmers have traditionally used this paradigm:

var callback = function(err, data) {
    if (err) { /* do something if there was an error */ }

    /* other logic here */

};

Why not simplify the function to accept only one parameter, which is either an error or an answer?

var callback = function(data) {
    if (isError(data)) { /* do something if there was an error */ }

    /* other logic here */

};

It seems easier. The only drawback I see is that functions cannot return errors as their actual estimated return value, but I find this to be an incredibly minor use case.

Why is an error template considered standard?

EDIT: Implementation isError:

var isError = function(obj) {
    try { return obj instanceof Error; } catch(e) {}
    return false;
};

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Answer 1

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request(url, (err, res, data) => {
  if (err) {
    // you have error
  } else {
    // you have both res and data
  }
});

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nodeStyle(params, function (err, data) {
  if (err) {
    // error
  } else {
    // success
  }
};

yourStyle(params, function (data) {
  if (isError(data)) {
    // error
  } else {
    // success
  }
};

promiseStyle(params)
  .then(function (data) {
    // success
  })
  .catch(function (err) {
    // error
  });

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Update

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• https://www.npmjs.com/package/errc

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npm install errc --save

:

var errc = require('errc');
var fs = require('fs');

var isError = function(obj) {
  try { return obj instanceof Error; } catch(e) {}
  return false;
};

var callback = function(data) {
  if (isError(data)) {
    console.log('Error:', data.message);
  } else {
    console.log('Success:', data);
  }
};

fs.readFile('example.txt', errc(callback));

:

• https://github.com/rsp/node-errc-example

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Answer 2

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