Unescaping HTML in JavaScript

Introduction

In web development, developers often work with HTML content that needs to be displayed in a web page. When this content is stored in a database or received from third-party systems, it may be escaped to avoid XSS (Cross-Site Scripting) attacks. Escaping HTML means converting special characters like < and > to their corresponding HTML entities such as < and >. In order to display the content in its original form, we need to unescape the HTML.

In JavaScript, there are several ways to unescape HTML. In this article, we will explore these methods and their differences.

Using the innerHTML Property

One common way to unescape HTML is to use the innerHTML property of an HTML element. Assuming we have an element with the ID "myElement", we can assign the escaped HTML to its innerHTML property and the browser will unescape it for us:

const myElement = document.getElementById("myElement");
const escapedHtml = "<p>Hello, World!</p>";
myElement.innerHTML = escapedHtml; // "Hello, World!"

Note that this method may not be safe if the HTML contains untrusted content, as it can lead to XSS attacks. Use it only when you can guarantee the safety of the HTML.

Using a DOM Parser

Another way to unescape HTML is to use a DOM parser to parse the HTML string and access its text content:

const escapedHtml = "<p>Hello, World!</p>";
const parser = new DOMParser();
const decodedHtml = parser.parseFromString(escapedHtml, "text/html").documentElement.textContent;
console.log(decodedHtml); // "Hello, World!"

This method is safer than the previous one as it only accesses the text content of the HTML, removing any potential script tags or malicious content.

Using a Regular Expression

A third way to unescape HTML is to use a regular expression to replace the escape sequences with their corresponding characters:

const escapedHtml = "<p>Hello, World!</p>";
const decodedHtml = escapedHtml.replace(/<|>|"|'/g, function(match) {
  switch (match) {
    case "<":
      return "<";
    case "&gt;":
      return ">";
    case "&quot;":
      return "\"";
    case "&#39;":
      return "'";
  }
});
console.log(decodedHtml); // "<p>Hello, World!</p>"

This method can be faster than the previous two, but it is also more error-prone as it requires manual handling of all possible escape sequences.

Conclusion

In this article, we have explored three ways to unescape HTML in JavaScript: using the innerHTML property, using a DOM parser, and using a regular expression. Each method has its own advantages and drawbacks, and should be used in the appropriate context. Remember to always validate and sanitize any HTML content before unescaping it to prevent XSS attacks.