Learn Functional Programming by Building a Spreadsheet - Step 35

Tell us what’s happening:

Describe your issue in detail here.
i need help, it says to " Start by declaring a rangeRegex variable and assign it a regular expression that matches A through J (the range of columns in your spreadsheet). Use a capture group with a character class to achieve this."
and it gives the error: " Your rangeRegex should use a capture group."

Your code so far

<!-- file: index.html -->
<!DOCTYPE html>
<html lang="en">
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <link rel="stylesheet" href="./styles.css" />
    <title>Functional Programming Spreadsheet</title>
    <div id="container">
    <script src="./script.js"></script>
/* file: styles.css */
#container {
  display: grid;
  grid-template-columns: 50px repeat(10, 200px);
  grid-template-rows: repeat(11, 30px);

.label {
  background-color: lightgray;
  text-align: center;
  vertical-align: middle;
  line-height: 30px;
/* file: script.js */
const isEven = num => num % 2 === 0;
const sum = nums => nums.reduce((acc, el) => acc + el, 0);
const average = nums => sum(nums) / nums.length;

const median = nums => {
  const sorted = nums.slice().sort((a, b) => a - b);
  const length = sorted.length;
  const middle = length / 2 - 1;
  return isEven(length)
    ? average([sorted[middle], sorted[middle + 1]])
    : sorted[Math.ceil(middle)];

const spreadsheetFunctions = {

const range = (start, end) => Array(end - start + 1).fill(start).map((element, index) => element + index);
const charRange = (start, end) => range(start.charCodeAt(0), end.charCodeAt(0)).map(code => String.fromCharCode(code));

/* User Editable Region */

const evalFormula = (x, cells) => {
  const idToText = id => cells.find(cell => cell.id === id).value;
const rangeRegex = /^[A-J]/;


/* User Editable Region */

window.onload = () => {
  const container = document.getElementById("container");
  const createLabel = (name) => {
    const label = document.createElement("div");
    label.className = "label";
    label.textContent = name;
  const letters = charRange("A", "J");
  range(1, 99).forEach(number => {
    letters.forEach(letter => {
      const input = document.createElement("input");
      input.type = "text";
      input.id = letter + number;
      input.ariaLabel = letter + number;
      input.onchange = update;

const update = event => {
  const element = event.target;
  const value = element.value.replace(/\s/g, "");
  if (!value.includes(element.id) && value.startsWith('=')) {


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Challenge Information:

Learn Functional Programming by Building a Spreadsheet - Step 35

You appear to have created this post without editing the template. Please edit your post to Tell us what’s happening in your own words.

You have a character class but no capture group (as stated by the hint)


"Parentheses group the regex between them. They capture the text matched by the regex inside them into a numbered group that can be reused with a numbered backreference. They allow you to apply regex operators to the entire grouped regex.

(abc){3} matches abcabcabc. First group matches abc."

So I need to create a regex that matches a cell id that can be either A2:B7 or C3:D4.
My regex looks like this:

const myRegex = /[A-J][0-9]+:[A-J][0-9]/g;

What is the purpose of using a capture group, I don’t quite understand where it should go.


Capture groups and back-references are some of the more fun features of regular expressions. You place a sub-expression in parentheses, you access the capture with \1 or $1… What could be easier?

For instance, the regex \b(\w+)\b\s+\1\b matches repeated words, such as regex regex, because the parentheses in (\w+) capture a word to Group 1 then the back-reference \1 tells the engine to match the characters that were captured by Group 1.

If you have further questions please open a new topic, thanks!