Calculating resistance of n devices - JavaScript

In Physics, the equivalent resistance of say 3 resistors connected in series is given by −

R = R1 + R2 + R3

And the equivalent resistance of resistors connected in parallel is given by −

R = (1/R1) + (1/R2) + (1/R3)

We are required to write a JavaScript function that takes a string having two possible values, 'series' or 'parallel' and then n numbers representing the resistance of n resistors.

And the function should return the equivalent resistance of these resistors.

Example

Let us write the code for this function.

const r1 = 5, r2 = 7, r3 = 9;
const equivalentResistance = (combination = 'parallel', ...resistors) => {
   if(combination === 'parallel'){
      return resistors.reduce((acc, val) => (1/acc) + (1/val));
   };
   return resistors.reduce((acc, val) => acc + val);
};
console.log(equivalentResistance('parallel', r1, r2, r3));

Output

Following is the output in the console −

3.0277777777777777