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freddie2025's solution

to ETL in the JavaScript Track

Published at Apr 03 2020 · 0 comments
Test suite


This exercise has changed since this solution was written.

We are going to do the Transform step of an Extract-Transform-Load.


Extract-Transform-Load (ETL) is a fancy way of saying, "We have some crufty, legacy data over in this system, and now we need it in this shiny new system over here, so we're going to migrate this."

(Typically, this is followed by, "We're only going to need to run this once." That's then typically followed by much forehead slapping and moaning about how stupid we could possibly be.)

The goal

We're going to extract some scrabble scores from a legacy system.

The old system stored a list of letters per score:

  • 1 point: "A", "E", "I", "O", "U", "L", "N", "R", "S", "T",
  • 2 points: "D", "G",
  • 3 points: "B", "C", "M", "P",
  • 4 points: "F", "H", "V", "W", "Y",
  • 5 points: "K",
  • 8 points: "J", "X",
  • 10 points: "Q", "Z",

The shiny new scrabble system instead stores the score per letter, which makes it much faster and easier to calculate the score for a word. It also stores the letters in lower-case regardless of the case of the input letters:

  • "a" is worth 1 point.
  • "b" is worth 3 points.
  • "c" is worth 3 points.
  • "d" is worth 2 points.
  • Etc.

Your mission, should you choose to accept it, is to transform the legacy data format to the shiny new format.


A final note about scoring, Scrabble is played around the world in a variety of languages, each with its own unique scoring table. For example, an "E" is scored at 2 in the Māori-language version of the game while being scored at 4 in the Hawaiian-language version.


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.


The Jumpstart Lab team http://jumpstartlab.com

Submitting Incomplete Solutions

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


import { transform } from './etl';

describe('Transform', () => {
  test('transforms one value', () => {
    const old = { 1: ['A'] };
    const expected = { a: 1 };


  xtest('transforms more values', () => {
    const old = { 1: ['A', 'E', 'I', 'O', 'U'] };
    const expected = {
      a: 1, e: 1, i: 1, o: 1, u: 1,


  xtest('transforms more keys', () => {
    const old = { 1: ['A', 'E'], 2: ['D', 'G'] };
    const expected = {
      a: 1, e: 1, d: 2, g: 2,


  xtest('transforms a full dataset', () => {
    const old = {
      1: ['A', 'E', 'I', 'O', 'U', 'L', 'N', 'R', 'S', 'T'],
      2: ['D', 'G'],
      3: ['B', 'C', 'M', 'P'],
      4: ['F', 'H', 'V', 'W', 'Y'],
      5: ['K'],
      8: ['J', 'X'],
      10: ['Q', 'Z'],
    const expected = {
      a: 1,
      b: 3,
      c: 3,
      d: 2,
      e: 1,
      f: 4,
      g: 2,
      h: 4,
      i: 1,
      j: 8,
      k: 5,
      l: 1,
      m: 3,
      n: 1,
      o: 1,
      p: 3,
      q: 10,
      r: 1,
      s: 1,
      t: 1,
      u: 1,
      v: 4,
      w: 4,
      x: 8,
      y: 4,
      z: 10,

// This is only a SKELETON file for the 'etl' exercise. It's been provided as a
// convenience to get you started writing code faster.

export const transform = (input) => {
  let map = new Map();

  for (let key in input) {
    let value = input[key];
    for (let i = 0; i < value.length; i++) {
      map.set(value[i].toLowerCase(), parseInt(key));

  return Object.fromEntries(map);

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