How to Safely Unescape HTML Entities in JavaScript?

Unescaping HTML Entities in JavaScript: A Comprehensive Guide

When working with web applications, it is often necessary to decode HTML entities that have been encoded for various reasons, such as security or compatibility. In JavaScript, the need to unescape HTML entities may arise, particularly when data is obtained from XML-RPC or other sources that encode characters for transmission.

One common issue that can occur is when strings returned by an XML-RPC backend contain HTML entities, but when these strings are inserted into HTML using JavaScript, they are rendered literally instead of as the intended HTML code. This indicates that the HTML entities are being escaped over the XML-RPC channel.

Unsafe Decoding Techniques to Avoid

Many methods for unescaping HTML entities in JavaScript have been proposed, but some of them pose significant security risks. For example, the following function:

function htmlDecode(input) {
  return input.replace(/&amp;/g, "&").replace(/</g, "<").replace(/>/g, ">");
}

While this method may seem to work initially, it fails to account for potential malicious intent. If the input string contained an unescaped HTML tag (e.g.,

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