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to Resistor Color Duo in the TypeScript Track

Published at Nov 02 2020 · 0 comments
Test suite


This exercise has changed since this solution was written.

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 { 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 enum BandColors {

export class ResistorColor {
  constructor(private readonly colors: BandColors[]) {
    if(colors.length < 2){
      throw new Error("At least two colors need to be present")

  public value(): number {
      return  this.colors[0] * 10 + this.colors[1];

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