readme.md

Composable middleware

Ever wanted to run some validation functions before another function is called? Use composable middleware, it's fun!

middleware.js

// compose fns together
const compose = (...fns) => fns.reduce((f, g) => (...args) => f(g(...args)))

// If `fn` evaluates to true call fn2 passing args through
const middleware = fn => fn2 => (...args) => fn(...args) && fn2(...args)

// 
// Example usage and tests
//

// create a middleware to ensure exactly two Args are passed to the function
const hasTwoArgs = middleware((...Args) => Args.length === 2)

// create a middleware to ensure that the first arg is an array
const firstArgIsArray = middleware(a => Array.isArray(a))

// compose the middleware together
const hasTwoFirstArray = compose(hasTwoArgs, firstArgIsArray)

// This function will only execute if there are exactly two args and the
// first arg is an array
const myValidatedFn = hasTwoFirstArray((a, b) => `It worked ${a} ${b}`)

// feature rich assertion library
const expect = t => ({ toEqual: v => v === t 
  ? `\u2714  Passed`
  : `\u274C  Failed. Expected "${t}" to equal "${v}"`
})

// tests
expect(myValidatedFn([1,2,3], 'something')).toEqual('It worked 1,2,3 something')
expect(myValidatedFn([1,2,3], 'something', 'bad')).toEqual(false)
expect(myValidatedFn('bad', 'something')).toEqual(false)
expect(myValidatedFn()).toEqual(false)
expect(myValidatedFn('bad')).toEqual(false)