functional-conditions

Making conditional statements in JavaScript functional

Installation

Using npm:

npm install @slicr97/functional-conditions

Using yarn:

yarn add @slicr97/functional-conditions

Usage

Import the functions you want to use:

import { $if, $switch, $tryCatch } from '@slicr97/functional-conditions';

Or, make them available globally by importing at the top of your entrypoint:

import '@slicr97/functional-conditions/globalize';

The $if function

This function provides a simple, pure wrapper around JavaScript's if statement. It takes three parameters:

1. The condition, which is checked for being truthy or falsy
2. The 'then'-case. This can be either a constant value or a function resolving into any return type. This case is executed if condition evaluates to true.
3. The 'else'-case. This can also be a constant or a function. This case is executed if condition evaluates to false.

The $switch function

This function emulates a wrapper around JavaScript's switch statement. It takes one option parameter, consisting of the following properties:

1. with is the value that is being evaluated
2. cases is an array of tuples. Each case consists of
3. c can be a constant value that will be compared to with or a function that takes with and returns either true or false
4. then can be a constant value that will be returned or a function that returns a value
5. default is the default value that is returned if no cases match. This can be either a constant value or a function that returns a value.

The $tryCatch function

This function wraps JavaScript's tryCatch statement. It takes an fn parameter which is a function that tries to execute. It also takes a second parameter, err, which can either be a constant value or a function that takes an error which can be used to format the error and return.

Examples

$if

import { $if } from '@slicr97/functional-conditions';

const a = 2;
const b = 3;

const message = $if (
  a > b,
  'a is larger than b',
  'a is not larger than b'
);

console.log(message); // Will log "a is not larger than b"

$switch

import { $switch } from '@slicr97/functional-conditions';

const age = 43;

const message = $switch ({
  with: age,
  cases: [
    [a => a > 80, 'You\'re very old'],
    [a => a > 60, 'You\'re pretty old'],
    [a => a > 40, 'You\'re not that old'],
    [a => a > 20, 'You\'re pretty young'],
    [a => a > 0, 'You\'re very young']
  ],
  default: 'You\'re less than 0 years old???'
});

console.log(message); // Will log "You're not that old"

$tryCatch

import {$tryCatch} from '@slicr97/functional-conditions';

const value = $tryCatch(
  () => 3 / 0,
  'Cannot divide by zero!'
);

console.log(value); // Will log "Cannot divide by zero!"

Considerations

Switch cases

Switch cases are checked sequentially and execution stops once the first valid case is reached. This means that if you have

[a => a > 20]

and

[a => a > 40]

in that order, the code could never step into the second case, as the first one also satisfies the condition.

Side effects

While it is not strictly necessary to pass pure functions into $if or $switch, I strongly encourage doing so. These functions were not built with effectful functions in mind and I won't guarantee that the functions will not be executed out of order.