Common Denominators.js

/*
Description:
Common denominators

You will have a list of rationals in the form

 { {numer_1, denom_1} , ... {numer_n, denom_n} } 
or

 [ [numer_1, denom_1] , ... [numer_n, denom_n] ] 
or

 [ (numer_1, denom_1) , ... (numer_n, denom_n) ] 
where all numbers are positive ints.

You have to produce a result in the form

 (N_1, D) ... (N_n, D) 
or

 [ [N_1, D] ... [N_n, D] ] 
or

 [ (N_1', D) , ... (N_n, D) ] 
or

{{N_1, D} ... {N_n, D}} 
depending on the language (See Example tests)

in which D is as small as possible and

 N_1/D == numer_1/denom_1 ... N_n/D == numer_n,/denom_n.
Example:

convertFracs [(1, 2), (1, 3), (1, 4)] `shouldBe` [(6, 12), (4, 12), (3, 12)]
Note for Bash
input is a string, e.g "2,4,2,6,2,8"

output is then "6 12 4 12 3 12"
*/

const gcd = (a, b) => b ? gcd(b, a % b) : a;
const lcm = (a, b) => a * b / gcd(a, b);

function convertFrac(arr) {
  const cd = arr.reduce((a, [_, d]) => lcm(d, a), 1);
  return arr.map(([n, d]) => `(${n * cd/d},${cd})`).join('');
}