thunk-shift-right v1.0.0

Wrap asynchronous thunks to shift callback parameters right

// Without `shiftCallbackParamsRight`

var thunk = thunkify(asyncFunc);

thunk(function (data) {
  // It's a bad idea to have the first parameter represent data.
});

// With `shiftCallbackParamsRight`

var thunk = shiftParamsRight(thunkify(asyncFunc));

thunk(function (err, data) {
  // Now, data is on the right, and `err` is always going to be null
});

Usage

Install thunk-shift-right using npm:

npm install thunk-shift-right

Then import it, and use it to wrap an asynchronous thunk (in this case, the asynchronous thunk is generated using thunkify):

var thunkify = require('thunkify');
var shiftCallbackParamsRight = require('thunk-shift-right');

var thunk = shiftCallbackParamsRight(function asyncFunc(callback) {
  setImmediate(function () {
    callback('Some valid, non-error data');
  });
});

Use case

This is especially useful with co, where it assumes that the first parameter passed in to the callback always represents an error, when in reality, it doesn't (the following code is using the ES6 syntax).

// Without `shiftCallbackParamsRight`

let thunk = thunkify(function (callback) {
  setImmediate(function () {
    // N.B.: the first parameter passed-in to the callback is NOT an error!
    // However, because of that, `co` will always assume that a non-falsy value
    // passed-in to the callback is an error!
    callback('Some valid, non-error data');
  });
});

co(function *() {
  const value = yield thunk();
  // -> **CRASH**! We have an error!

  // The following code, and any additional code in this function will not be
  // run because the above code raised an exception!
  console.log(value);
});

// With `shifParamsRight`

let thunk = shiftCallbackParamsRight(thunkify(function (callback) {
  setImmediate(function () { callback('Some valid, non-error data'); })
}));

co(function *() {
  const value = yield thunk();

  console.log(value);
  // -> 'Some valid, non-error data'
});

License

thunk-shift-right is MIT-Licensed