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to Resistor Color Duo in the TypeScript Track

Published at May 16 2021 · 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.

The first 2 bands of a resistor have a simple encoding scheme: each color maps to a single number. 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 band colors are encoded as follows:

  • Black: 0
  • Brown: 1
  • Red: 2
  • Orange: 3
  • Yellow: 4
  • Green: 5
  • Blue: 6
  • Violet: 7
  • Grey: 8
  • White: 9

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 TypeScript to install the necessary dependencies:



Install assignment dependencies:

$ yarn install

Making the test suite pass

Execute the tests with:

$ yarn 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 xit to it.


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 { ResistorColor } from './resistor-color-duo'

describe('Resistor Colors', () => {
  it('Brown and black', () => {
    const resistorColor = new ResistorColor(['brown', 'black'])

  xit('Blue and grey', () => {
    const resistorColor = new ResistorColor(['blue', 'grey'])

  xit('Yellow and violet', () => {
    const resistorColor = new ResistorColor(['yellow', 'violet'])

  xit('Orange and orange', () => {
    const resistorColor = new ResistorColor(['orange', 'orange'])

  xit('Ignore additional colors', () => {
    const resistorColor = new ResistorColor(['green', 'brown', 'orange'])

  xit('Throws error when not enough colors', () => {
    expect(() => new ResistorColor(['green'])).toThrowError(
      'At least two colors need to be present'
export class ResistorColor {

  private colors: string[];

  constructor (colors: string[]) {
    if (colors.length < 2) {
      throw Error('At least two colors need to be present');

    // Ignore additional colors
    this.colors = colors.splice(0, 2);
  public value(): number {
    let result = ""
    for (let color of this.colors) {
      result += colorCode(color);
    return Number.parseInt(result)

export const colorCode = (color: string) => {
  return COLORS.indexOf(color)

export const COLORS = [

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