TypeScript Options-object "Currying"

Curry a function's default options.

Since working with TypeScript I've moved to mostly having functions that only accepts 1 options argument as then the args get named, order of args doesn't matter, and you can add new options without breaking the API.

Sometimes it's nice to compose a new function with default values set. This lib does that.

• How to use
  • Examples
    • Happy path
    • Type safety showcase
• Local Development
  • yarn start
  • yarn build
  • yarn test

How to use

npm i options-curry --save

yarn add options-curry

Examples

Happy path

import { withDefaults } from 'options-curry';

// Create function with an options object
function fn({ foo, bar }: { foo: string; bar: string }) {
  return { foo, bar };
}

// Compose new function where options are pre-set
const fnWithDefaults = withDefaults(fn, {
  foo: 'foo',
});

// `foo`-key is now optional in `fnWithDefaults`
console.log(fnWithDefaults({ bar: 'bar' })); // ➡️ { foo: 'foo', bar: 'bar' }
console.log(fnWithDefaults({ bar: 'bar', foo: 'x' })); // ➡️ ️{ foo: 'x', bar: 'bar' }

// We can compose a new function from our function with defaults
const composedFn = withDefaults(fnWithDefaults, { bar: 'bar' });
console.log(composedFn({})); // ➡️ `{ foo: 'foo', bar: 'bar' }`

Type safety showcase

import { withDefaults } from 'options-curry';

// Create function with an options object
function fn({ foo, bar }: { foo: string; bar: string }) {
  return { foo, bar };
}

// Compose new function where options are pre-set
const fnWithDefaults = withDefaults(fn, {
  foo: 'foo',
});

// Input arguments are typed
fnWithDefaults({
  bar: 1, // ❌ Error "Type 'number' is not assignable to type 'string'"
});

// ReturnType is typed
const ret = fnWithDefaults({ bar: 'x' });
console.log(ret.nope); // ❌ Error: "Property 'nope' does not exist on type '{ foo: string; bar: string; }"

Local Development

(This project was bootstrapped with TSDX.)

Below is a list of commands you will probably find useful.

yarn start

Runs the project in development/watch mode. Your project will be rebuilt upon changes. TSDX has a special logger for you convenience. Error messages are pretty printed and formatted for compatibility VS Code's Problems tab.

yarn build

Bundles the package to the dist folder. The package is optimized and bundled with Rollup into multiple formats (CommonJS, UMD, and ES Module).

yarn test

Runs the test watcher (Jest) in an interactive mode. By default, runs tests related to files changed since the last commit.