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JavaScript Regular Expressions in JavaScript Validating a Form Form Validation

Brian Foley
Brian Foley
8,440 Points

RegEx help please

Hello, I need a little help with what I'm doing wrong with this Regular Expressions challenge. Here's the challenge and below is my answer attempt:

In this challenge you'll write a validator for a hexadecimal string used to set a CSS color. Hexadecimal values for css colors start with a pound sign, or hash (#), then six characters that can either be a numeral or a letter between A and F, inclusive. Two examples of these strings would be #FF4569 and #578E9A. For this step of the challenge, write a regular expression that will match any hexadecimal string and store it in a variable named hexRegEx. The regex should be case-insensitive. Assume that the string will always be 7 characters.

Here’s my answer attempt:

function isValidHex(text) { const hexRegEx = /\w{7}/i.test(text); }

// Type inside this function
function isValidHex(text) {
  const hexRegEx = /\w{7}/i.test(text); 

const hex = document.getElementById("hex");
const body = document.getElementsByTagName("body")[0];

hex.addEventListener("input", e => {
  const text = e.target.value;
  const valid = isValidHex(text);
  if (valid) {
    body.style.backgroundColor = "rgb(176, 208, 168)";
  } else {
    body.style.backgroundColor = "rgb(189, 86, 86)";
<!DOCTYPE html>

    <title>DOM Manipulation</title>
<link rel="stylesheet" href="style.css" />

    <div id="content">
        <p>Enter a valid hex value below to make the screen turn green.</p>
        <input type="text" id="hex">
    <script src="app.js"></script>


1 Answer

Your solution will technically work to find a hexadecimal value, but it will also find any other 7 character value as well. The question is looking for a regular expression that will only work for a hexadecimal css value.

Here is a solution that I came up with:

function isValidHex(text) {
     const hexRegEx = /^#[a-f0-9]{6}$/i;

This first step only asks for the variable hexRegEx to contain the regular expression, so it won't work if you include the .test() method at the end.

We know that the regular expression will always be 7 characters long so we constrain it with ^ at the beginning and $ at the end. We also know that the regular expression needs to start with a # so we include it at the beginning.

We know that the next characters need to be either a letter between A-F or a number between 0-9 so we state these constraints by writing [a-f0-9]

We also know that we need 6 of these letters/number so we write {6}

And finally, we know that the regex should be case-insensitive so we include i after the regular expression.

Hope this short explanation helps!

Umidjon Khaitov
Umidjon Khaitov
8,884 Points

Very clear explanation, thank you!