# 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."

``````<!-- file: index.html -->
<!DOCTYPE html>
<html lang="en">
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<body>
<div id="container">
<div></div>
</div>
<script src="./script.js"></script>
</body>
</html>
``````
``````/* 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)];
}

sum,
average,
median
}

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 */

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

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

}
}
``````

User Agent is: `Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36`

### 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)

https://www.regular-expressions.info/refcapture.html

"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.

https://www.rexegg.com/regex-capture.html

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!