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SergiiVlasiuk's solution

to Resistor Color Duo in the JavaScript Track

Published at Apr 06 2020 · 0 comments
Test suite

If you want to build something using a Raspberry Pi, you'll probably use resistors. For this exercise, you need to know two things about them:

  • Each resistor has a resistance value.
  • Resistors are small - so small in fact that if you printed the resistance value on them, it would be hard to read.

To get around this problem, manufacturers print color-coded bands onto the resistors to denote their resistance values. Each band has a position and a numeric value. For example, if they printed a brown band (value 1) followed by a green band (value 5), it would translate to the number 15.

In this exercise you are going to create a helpful program so that you don't have to remember the values of the bands. The program will take color names as input and output a two digit number, even if the input is more than two colors!

The colors are mapped to the numbers from 0 to 9 in the sequence: Black - Brown - Red - Orange - Yellow - Green - Blue - Violet - Grey - White

From the example above: brown-green should return 15 brown-green-violet should return 15 too, ignoring the third color.


Go through the setup instructions for Javascript to install the necessary dependencies:



Install assignment dependencies:

$ npm install

Making the test suite pass

Execute the tests with:

$ npm test

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by changing xtest to test.


Maud de Vries, Erik Schierboom https://github.com/exercism/problem-specifications/issues/1464

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


import { decodedValue } from './resistor-color-duo.js';

describe('Resistor Colors', () => {
  test('Brown and black', () => {
    expect(decodedValue(['brown', 'black'])).toEqual(10);

  xtest('Blue and grey', () => {
    expect(decodedValue(['blue', 'grey'])).toEqual(68);

  xtest('Yellow and violet', () => {
    expect(decodedValue(['yellow', 'violet'])).toEqual(47);

  xtest('Orange and orange', () => {
    expect(decodedValue(['orange', 'orange'])).toEqual(33);

  xtest('Ignore additional colors', () => {
    expect(decodedValue(['green', 'brown', 'orange'])).toEqual(51);
// This is only a SKELETON file for the 'Resistor Color Duo' exercise. It's been provided as a
// convenience to get you started writing code faster.

function indexOf(colorName) {
    const ind = COLORS.indexOf(colorName);
    return ind >= 0 ? `${ind}` : '';
export const decodedValue = (arr) => {
    let res = '';
    for (let ind = 0; ind < arr.length && ind < 2; ind++) {
        res += indexOf(arr[ind]);
    return +res;

export const COLORS = ["black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "grey", "white"];

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