How to decode HTML entities using jQuery?

Solution 1:

Security note: using this answer (preserved in its original form below) may introduce an XSS vulnerability into your application. You should not use this answer. Read lucascaro's answer for an explanation of the vulnerabilities in this answer, and use the approach from either that answer or Mark Amery's answer instead.

Actually, try

var encodedStr = "This is fun & stuff";
var decoded = $("<div/>").html(encodedStr).text();
console.log(decoded);

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div/>

Solution 2:

Without any jQuery:

function decodeEntities(encodedString) {
  var textArea = document.createElement('textarea');
  textArea.innerHTML = encodedString;
  return textArea.value;
}

console.log(decodeEntities('1 & 2')); // '1 & 2'

This works similarly to the accepted answer, but is safe to use with untrusted user input.

Security issues in similar approaches

As noted by Mike Samuel, doing this with a <div> instead of a <textarea> with untrusted user input is an XSS vulnerability, even if the <div> is never added to the DOM:

function decodeEntities(encodedString) {
  var div = document.createElement('div');
  div.innerHTML = encodedString;
  return div.textContent;
}

// Shows an alert
decodeEntities('<img src="nonexistent_image" onerror="alert(1337)">')

However, this attack is not possible against a <textarea> because there are no HTML elements that are permitted content of a <textarea>. Consequently, any HTML tags still present in the 'encoded' string will be automatically entity-encoded by the browser.

function decodeEntities(encodedString) {
    var textArea = document.createElement('textarea');
    textArea.innerHTML = encodedString;
    return textArea.value;
}

// Safe, and returns the correct answer
console.log(decodeEntities('<img src="nonexistent_image" onerror="alert(1337)">'))

Warning: Doing this using jQuery's .html() and .val() methods instead of using .innerHTML and .value is also insecure* for some versions of jQuery, even when using a textarea. This is because older versions of jQuery would deliberately and explicitly evaluate scripts contained in the string passed to .html(). Hence code like this shows an alert in jQuery 1.8:

//<!-- CDATA
// Shows alert
$("<textarea>")
.html("<script>alert(1337);</script>")
.text();

//-->

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.2.3/jquery.min.js"></script>

_{* Thanks to Eru Penkman for catching this vulnerability.}