functional compositions

functional-composition.js

//*********************** as libraries ***********************
const pipe = (...functions) => v => functions.reduce((y, f) => f(y), v)
const mapFn = f => arr => arr.map(f)
const trace = key => value => console.log(`${key} : ${value}`)

// TODO: need improvements
const expect = actual => ({
	toBe: expected => {
		if (Array.isArray(expected)) {
			if (expected.length > 0 && expected.length === actual.length) {
				return expected.every((e, i) => e === actual[i])
			}
			return false
		} else if (typeof expected === 'number') {
			return actual === expected
		}

		throw "is not able to maintain."
	}
});

//*********************** [TEST] multiply by 2 ***********************
const multiply2 = pipe(
	mapFn(x => x * 2)
)

console.log(
    expect(multiply2([1, 2, 3])).toBe([2, 4, 6]),
)

//*********************** [TEST] add with 5 ***********************
const add5 = pipe(
	mapFn(x => x +5)
)

console.log(
    expect(add5([1,2,3])).toBe([6, 7, 8]),
)

//*********************** [TEST] convert first letter of string to upper case ***********************
const firstLetterUpper = pipe(
    mapFn(s => s[0].toUpperCase() + s.substring(1)),
)

console.log(
    expect(firstLetterUpper(['milad', 'hello'])).toBe(['Milad', 'Hello']),
)