chooser
A small, but fully featured, library that aims to completely replace switch case logic (which is unfavorable in Functional Programming), with a simple declarative API for setting up a predefined map of cases, and choosing a result from it based on input.
Features
- Map cases to results.
- Map multiple cases to the same result.
- Customize the equality function used to produce a match, either at case declaration, or at the time of input.
- Refer from one case to another by
ref-ing its index. - Refer from one case to another by
use-ing itswhenvalue. - Leverage the lazy nature of functions to compute a result only when needed, and not at the time of the case declaration.
- If a function is intended to be returned as is, it can be put under the
eagerkey. - Written in TypeScript and bundled with Rollup, featuring:
- A CommonJS module for node.
- An ES Module for node.
Installation
$ npm install chooserUsage
const chooser = require('chooser');
const choose = chooser([
{ when: [1, 2], then: 'one' },
{ when: 3, then: 'two' },
{ when: 4, ref: 0 },
{ when: 5, use: 3 },
]);
choose(1); // => 'one'
choose(2); // => 'one'
choose(3); // => 'two'
choose(4); // => 'one'
choose(5); // => 'two'Terminology
Choices
The choices parameter should be either a plain js object with keys (for cases) and values (for results), or an array of choice objects adhering to the choice schema.
Choice
The choice objects are objects that adhere to the following schema:
type Choice = {
when: any;
then?: any;
ref?: number;
use?: any;
eager?: Function;
};Examples
Basic example:
const chooser = require('chooser');
const choose = chooser([
{ when: [1, 2], then: 'one' },
{ when: 3, then: 'two' },
{ when: 4, ref: 0 },
{ when: 5, use: 3 },
]);
choose(1); // => 'one'
choose(2); // => 'one'
choose(3); // => 'two'
choose(4); // => 'one'
choose(5); // => 'two'Leveraging lazy evaluation:
const chooser = require('chooser');
const choose = chooser([
{ when: 1, then: () => 'one' },
{ when: 2, then: () => 'two' },
]);
choose(1); // => 'one'
choose(2); // => 'two'Overriding lazy evaluation to return the function as is:
const chooser = require('chooser');
const fn = () => 'one';
const choose = chooser([
{ when: 1, then: fn },
{ when: 2, eager: fn },
]);
choose(1); // => 'one'
choose(2); // => Function: fnUsing a plain object:
const chooser = require('chooser');
const choose = chooser({
1: 'one',
2: 'two',
});
choose(1); // => 'one'
choose('1'); // => 'one'
choose(2); // => 'two'
choose('2'); // => 'two'Note: When using a plain object without specifying an
equalityFn(see below), the input is automatically converted to a string.
Using use shorthand in plain objects:
const choose = chooser({
1: 'one',
2: 'two',
3: '{#2}',
});
choose(1); // => 'one'
choose(2); // => 'two'
choose(3); // => 'two'Using ref shorthand in plain objects:
const chooser = require('chooser');
const choose = chooser({
1: 'one',
2: 'two',
3: '{$0}',
});
choose(1); // => 'one'
choose(2); // => 'two'
choose(3); // => 'one'Note: A caveat of using a plain object as
choicesis that in the case of numbered keys, the keys are automatically sorted by the language. This can lead to wrongrefs.
Demonstrating the sorted keys problem:
const chooser = require('chooser');
const choose = chooser({
2: 'two',
1: 'one',
3: '{$0}',
});
choose(3); // => 'one' instead of the usually expected 'two'Providing a custom equalityFn at case declaration:
const chooser = require('chooser');
const equalityFn = (input, when) => input.nested.value == when;
const choose = chooser(
[
{ when: 1, then: 'one' },
{ when: 2, then: 'two' },
],
undefined,
equalityFn,
);
const obj1 = { nested: { value: 1 } };
const obj2 = { nested: { value: 2 } };
choose(obj1); // => 'one'
choose(obj2); // => 'two'Providing a custom equalityFn at the time of input:
const equalityFnPerson = (input, when) => input.person.age == when;
const equalityFnDog = (input, when) => input.dog.age == when;
const choose = chooser([
{ when: 28, then: 'I am 28 years old!' },
{ when: 2, then: 'Woof woof!' },
]);
const data = {
person: { age: 28 },
dog: { age: 2 },
};
choose(data, equalityFnPerson); // => 'I am 28 years old!'
choose(data, equalityFnDog); // => 'Woof woof!'Specifying a defaultValue:
const chooser = require('chooser');
const choose = chooser(
[
{ when: 1, then: 'one' },
{ when: 2, then: 'two' },
],
'default string',
);
choose(3); // => 'default string'Closing Notes
Thank you for using this library. I hope it helps you write better, more declarative code, faster, without any duplication, or resorting to functions with switch cases, or weak mapper functions.
