Below are three functions that need to be composed and give us the output 30:
const add = (a) => a + 10;
const mul = (a) => a * 10;
const divide = (a) => a / 5;
// How to implement `compositionFunction`?
compositionFunction(add, mul, divide)(5);
//=> 30
Expected output is 30 because:
5 + 10 = 15
15 * 10 = 150
150 / 5 = 30
Something like this
const add = (a) => a + 10 ;
const mul = (a) => a * 10 ;
const divide = (a) => a / 5 ;
// How to use this function -----
const customComposeFn = (...f) => v => f.reduce((res, f) => f(res), v)
console.log(customComposeFn(add, mul, divide)(5));There are two flavours of function composition:
pipecomposeHere's a recursive implementation just for fun:
This assumes that there are at least two functions to compose
const compose = (...fn) => {
const [[f, g], x] = [fn.slice(-2), fn.slice(0, -2)];
const h = a => f(g(a));
return x.length ? compose(...x, h) : h;
}
const pipe = (...fn) => {
const [f, g, ...x] = fn;
const h = a => g(f(a));
return x.length ? pipe(h, ...x) : h;
}
Let's try:
const foo = x => x + 'foo';
const bar = x => x + 'bar';
const baz = x => x + 'baz';
pipe(foo, bar, baz)('');
//=> 'foobarbaz'
compose(foo, bar, baz)('');
//=> 'bazbarfoo'
const add = (a) => a + 10;
const mul = (a) => a * 10;
const divide = (a) => a / 5;
const customComposeFn = (...fn) => {
return function (arg) {
if (fn.length > 0) {
const output = fn[0](arg);
return customComposeFn(...fn.splice(1))(output);
} else {
return arg;
}
};
};
const res = customComposeFn(add, mul, divide)(5);
console.log(`res`, res);