rarity

Continuation tools for callbacks arity.

1 - Carry arguments

Here is some shitty code:

function(cb) {
    var aVar = 1;
    someFunction(function(err, result) {
        // Mix results from previous scope with new results
        cb(err, aVar, result);
    });
}

Here is some improved version, using rarity:

function(cb) {
    var aVar = 1;
    someFunction(rarity.carry([aVar], cb));
}

Arguments passed in the array will be carried between the first argument of the original callback (the error, in node convention) and all the others.

Documentation

rarity.carry(arrayOfArgumentsToAddBetweenErrorAndOriginal, cb)

If you pass something else than an array, it will be automatically wrapped in an array: rarity.carry(value, cb) => rarity.carry([value], cb) => cb(err, value, ...arguments)

2 - Slice arguments

Did you ever find yourself writing shitty code such as this one:

someShittyFunction(function(err, uselessArgument, anotherUselessArgument) {
    cb(err);
});

To minimize the quantity of arguments sent over to your next function (async.waterfall anyone?)

rarity allow you to easily control this behavior:

// Generate a wrapper function around cb, only forwarding the first parameter.
someShittyFunction(rarity.slice(1, cb));

Documentation

rarity.slice(maxNumberOfArgumentsToForward, cb)

Without rarity

var async = require('async');
 
async.waterfall([
    function callShittyLib(cb) {
        someShittyFunction(cb);
    },
    function handleResults(result, uselessArgument, anotherUselessArgument, cb) {
        // When writing your function, you need to check the documentation regarding the number of arguments you'll receive.
        // Boring.
        stuff();
        cb();
    }
], process.exit);

With rarity

var async = require('async');
var rarity = require('rarity');
 
async.waterfall([
    function callShittyLib(cb) {
        // Slice after the first two arguments (err and results), discard all others
        someShittyFunction(rarity.slice(2, cb));
    },
    function handleResults(result, cb) {
        // We only get result, not the other parameters (err was handled by the `async` lib)
        stuff();
        cb();
    }
], process.exit);

3 - Pad arguments

When using some shitty-backported lib, for instance factory-lady, you'll need to pad your queries with a first additional argument representing a fake error, making it compatible with all the node ecosystem.

The following code:

someShittyFunction(function(result) {
    cb(null, result);
});

Will become, using rarity:

// Wraps cb with a new function, sending null as the first argument.
someShittyFunction(rarity.pad([null], cb));

Documentation

rarity.pad(arrayOfArgumentsToPad, cb)

4 - Carry and slice

Specific use case, combining rarity.carry and rarity.slice:

The following code:

function(cb) {
    var aVar = 1;
    someFunction(function(err, result, useless) {
        cb(err, aVar, result);
    });
}

Will become, using rarity:

function(cb) {
    var aVar = 1;
    someFunction(rarity.carryAndSlice([aVar], 3, cb));
}

Documentation

rarity.carryAndSlice(arrayOfArgumentsToAddBetweenErrorAndOriginal, maxNumberOfArgumentsToForward, cb)

Installation

npm install rarity

You're done. Now go write some shitty code.

Why the shitty name?

rarity is short for reduce arity. Also, arity was already created on npm.