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1.1.0 • Public • Published


Curry any function with placeholder support

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curriable provides a curry method that is highly performant with a small footprint (578 bytes minified+gzipped). You can call the method with any combination of parameters (one at a time, all at once, or any number in between), and placeholders are supported.

If fn is the curried function and _ is the placeholder value, the following are all equivalent:

  • fn(1)(2)(3)
  • fn(1)(2, 3)
  • fn(1, 2)(3)
  • fn(1, 2, 3)
  • fn(_, 2, 3)(1)
  • fn(_, _, 3)(1)(2)
  • fn(_, _, 3)(1, 2)
  • fn(_, 2)(1)(3)
  • fn(_, 2)(1, 3)
  • fn(_, 2)(_, 3)(1)


You can use the default import:

import curry from "curriable";
const fn = curry((a, b, c) => [a, b, c]);
console.log(fn("a", curry.__, "c")("b")); // ["a", "b", "c"]
const original = curry.uncurry(fn);
console.log(original("a")); // ["a", undefined, undefined]

Or the named imports:

import { __, curry, uncurry } from "curriable";
const fn = curry((a, b, c) => [a, b, c]);
console.log(fn("a", __, "c")("b")); // ["a", "b", "c"]
const original = uncurry(fn);
console.log(original("a")); // ["a", undefined, undefined]


The curry method has the following signature:

function curry(fn: functionarity: number = fn.length) => function;

arity defaults to be the length provided by fn.length, but be aware this can cause unusual behavior with default parameters or use of rest parameters. See the documentation on Function.length for more details.

Rest parameters

console.log(function(...args) {}.length); // 0 arity computed

When using rest with curried functions, you should pass a second parameter to explicitly declare the correct arity:

const fn = (...args) => [a, b, c];
const curried = curry(fn, 3);
console.log(curried("a")("b")("c")); // ["a", "b", "c"]

Default parameters

console.log(function(a, b = 1, c) {}.length); // 1 arity computed

Default parameters are very rare use-case with curried functions, but it is possible to trigger them if you declare an explicit arity and explicitly pass undefined for that parameter:

const fn = (a, b = 1, c) => [a, b, c];
const curried = curry(fn, 3);
console.log(curried("a")(undefined)("c")); // ["a", 1, "c"]

Yes, this is weird, but it is very difficult (impossible?) to distinguish between a parameter being undefined through not being called yet in the curry chain vs being undefined by not being provided an explicit value. Explicitly passing undefined provides that distinction.


The function uncurry is also available on both the default export and as a named export, and this function will return the original (uncurried) fn passed to curry.

const curried = curry((a, b, c) => [a, b, c]);
console.log(curried("a")); // function() {}
const uncurried = uncurry(fn);
console.log(uncurried("a")); // ["a", undefined, undefined]


All values provided are the number of operations per second (ops/sec) calculated by the Benchmark suite. The same function was curried and tested passing each parameter individually, passing all at once, and using placeholders.

Benchmarks were performed on an i7 8-core Arch Linux laptop with 16GB of memory using NodeJS version 8.9.4.

Passing each parameter in curried calls

Library Operations / second Relative margin of error
curriable 1,632,076 1.43%
ramda 1,041,570 1.15%
lodash 138,685 0.88%

Passing all parameters in one call

Library Operations / second Relative margin of error
curriable 21,517,188 1.36%
ramda 10,064,677 0.97%
lodash 8,031,747 1.18%

Using placeholder parameters in curried calls

Library Operations / second Relative margin of error
curriable 2,577,105 1.02%
ramda 1,309,428 1.02%
lodash 204,268 0.77%


Standard stuff, clone the repo and npm install dependencies. The npm scripts available:

  • benchmark => run the benchmark suite pitting curriable against other libraries in common use-cases
  • clean => run clean:lib, clean:es, and clean:dist
  • clean:dist => run rimraf on the dist folder
  • clean:es => run rimraf on the es folder
  • clean:lib => run rimraf on the lib folder
  • dev => run webpack dev server to run example app (playground!)
  • dist => runs clean:dist and build
  • lint => runs ESLint against all files in the src folder
  • lint:fix => runs `lint``, fixing any errors if possible
  • prepublish => runs compile-for-publish
  • prepublish:compile => run lint, flow, test:coverage, transpile:lib, transpile:es, and dist
  • test => run AVA test functions with NODE_ENV=test
  • test:coverage => run test but with nyc for coverage checker
  • test:watch => run test, but with persistent watcher
  • transpile:es => run babel against all files in src to create files in es, preserving ES2015 modules (for pkg.module)
  • transpile:lib => run babel against all files in src to create files in lib


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