ffn

Turns arrays and values into Filtering Functions.

Many projects use callbacks to filter values. Sometimes this filtering involves complex conditions that need a function. Other times one just wants to test if the value equals another, or if the value appears in an array of acceptable values. Instead of making your project’s end-users write filters like x => x === 'value' or x => ['ok', 'also ok'].includes(x), let them provide the value or the array directly, and ffn will turn it into a filtering function.

Installation

Requires Node.js 6.0.0 or above.

npm i ffn

API

The module exports a single function.

Parameters

1. f (any): A Function, an Array, or some other value.
2. Object argument:
   • Optional: blacklist (bool): Set to true if ffn is being used to create a blacklist. This will make falsey values test true when f is undefined. Defaults to false.

Return Values

• If f is a Function: returns f
• If f is omitted or otherwise undefined: returns a function that tests whether its argument is truthy (unless blacklist is true)
• If f is an Array: returns a function that tests whether its argument is included in f
• Otherwise: returns a function that tests whether its argument is strictly equal to f

Example

const ffn = require('ffn')

const arr = [1, 2, 3, 4, 5]

// ffn returns functions as-is
arr.find(ffn(x => x % 2 === 0)) // 2

// ffn creates a function which checks for inclusion in the array
arr.find(ffn([4, 5])) // 4

// ffn creates a function which checks for equality with the value
arr.find(ffn(3)) // 3

Related

For more projects like this, check out the xfn family of modules.