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JavaScript Regular Expressions in JavaScript Validating a Form Form Validation

RegEx

// Type inside this function function isValidHex(text) { let hexRegEx = /^#\d{3}[A-Za-z]\d{1}[A-Za-z]$/; // Not Working return hexRegEx.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)"; } });

app.js
// Type inside this function
function isValidHex(text) {
  let hexRegEx = /^#\d{3}[A-Za-z]\d{1}[A-Za-z]$/;
  return hexRegEx.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)";
  }
});
index.html
<!DOCTYPE html>
<html>

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

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

</html>

2 Answers

Steven Parker
Steven Parker
231,110 Points

Let's break down the regex you show here:

  • ^# :point_left: starting with a # sign...
  • \d{3} :point_left: then 3 digits ...
  • [A-Za-z] :point_left: then any letter...
  • \d{1} :point_left: then one more digit...
  • [A-Za-z]$ :point_left: and ending with any letter

So this would allow "#802B3C" but not "#00FF00" (pure green). And it would allow "#123J4W" (not hex)

The actual regex you want is much simpler:

  • start with the # sign (that part was OK)
  • then allow characters that can be a digit OR a letter, but only up to "F"
  • and specifically six of those

Thank you Steven.

Steven Parker
Steven Parker
231,110 Points

Joseph Monreal — Glad to help. You can mark a question solved by choosing a "best answer".
And happy coding!