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zaetrik/compose.ts

Created June 4, 2020 12:59
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Compose Functions
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compose.ts
const composeLeftToRight = <F extends (x: any) => any>(...fns: Array<F>) => (
...[x]: Parameters<F>
): ReturnType<F> => fns.reduce((y, f) => f(y), x);
const composeRightToLeft = <F extends (x: any) => any>(...fns: Array<F>) => (
...[x]: Parameters<F>
): ReturnType<F> => fns.reduceRight((y, f) => f(y), x);
const addTwo = (x: number) => x + 2;
const double = ( x: number) => x * 2;
const doubleThenAdd = composeRightToLeft(addTwo, double);
console.log(doubleThenAdd(4)); // 10
const addThenDouble = composeLeftToRight(addTwo, double);
console.log(addThenDouble(4)); // 12
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