How Can I Safely Unescape HTML Entities in JavaScript?

Unescaping HTML Entities in JavaScript

Problem:

When receiving HTML strings from an XML-RPC backend, they render literally instead of being rendered as HTML elements. This suggests that the HTML is being escaped over the XML-RPC channel.

Solution Using DOMParser:

To correctly unescape HTML entities in JavaScript without introducing security vulnerabilities, it is recommended to use the DOMParser interface. DOMParser creates a DOM tree from the provided HTML string, which can then be used to retrieve the unescaped text content.

Here's an updated version of the htmlDecode function that utilizes DOMParser:

function htmlDecode(input) {
  var doc = new DOMParser().parseFromString(input, "text/html");
  return doc.documentElement.textContent;
}

The following examples demonstrate how to use the updated function:

console.log(htmlDecode("<img src='myimage.jpg'>"));
// "<img src='myimage.jpg'>"

console.log(htmlDecode("<img src='dummy' onerror='alert(/xss/)'>"));
// ""

In the second example, the potentially malicious HTML string is unescaped correctly, resulting in an empty string to prevent cross-site scripting (XSS) vulnerabilities.

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