html-escaper

What is html-escaper?

The html-escaper npm package is designed to escape and unescape HTML entities. It is useful for preventing XSS attacks by sanitizing user input or for properly displaying text that includes characters that are reserved in HTML.

What are html-escaper's main functionalities?

Escape HTML

Escapes HTML entities to prevent execution of potentially harmful scripts and to display HTML tags as plain text.

const { escape } = require('html-escaper');
const escapedString = escape('<div>Hello & Welcome!</div>');
console.log(escapedString); // &lt;div&gt;Hello &amp; Welcome!&lt;/div&gt;

Unescape HTML

Unescapes HTML entities to convert them back to their original characters, which is useful for rendering text that was previously escaped.

const { unescape } = require('html-escaper');
const unescapedString = unescape('<div>Hello & Welcome!</div>');
console.log(unescapedString); // <div>Hello & Welcome!</div>

Other packages similar to html-escaper

he

The 'he' package is a robust HTML entity encoder/decoder written in JavaScript. It supports all named character references defined in HTML, handling even obscure and rare entities. It is more comprehensive than html-escaper but might be larger in size.

escape-html

The 'escape-html' package is a simple and fast utility for escaping HTML entities. It is smaller and more lightweight than html-escaper, but it only provides the escaping functionality and does not include unescaping.

entities

The 'entities' package is another library for encoding and decoding HTML entities. It supports a wide range of character entities and offers both escaping and unescaping functionalities, similar to html-escaper, but with additional options for handling different document types.

README

html-escaper

A simple module to escape/unescape common problematic entities.

Go sloppy if you like!

If you'd like to deal with any kind of input, including null or undefined, and even symbol kind, check html-sloppy-escaper out: it's this very same module, except it never throws errors 👍

V3 ESM Only Release

The version 3 of this module ditches entirely legacy browsers and nodejs with broken loaders, such as v13.0.0 and v13.1.0.

As the code is basically identical, simply stick with version 2 if you have any issue with this one 👋

How

This package is available in npm so npm install html-escaper is all you need to do, using eventually the global flag too.

Once the module is present

import {escape, unescape} from 'html-escaper';

escape('string');
unescape('escaped string');

Why

there is basically one rule only: do not ever replace one char after another if you are transforming a string into another.

// WARNING: THIS IS WRONG
// if you are that kind of dev that does this
function escape(s) {
  return s.replace(/&/g, "&")
          .replace(/</g, "&lt;")
          .replace(/>/g, "&gt;")
          .replace(/'/g, "&#39;")
          .replace(/"/g, "&quot;");
}

// you might be the same dev that does this too
function unescape(s) {
  return s.replace(/&amp;/g, "&")
          .replace(/&lt;/g, "<")
          .replace(/&gt;/g, ">")
          .replace(/&#39;/g, "'")
          .replace(/&quot;/g, '"');
}

// guess what we have here ?
unescape('&amp;lt;');

// now guess this XSS too ...
unescape('&amp;lt;script&amp;gt;alert("yo")&amp;lt;/script&amp;gt;');

The last example will produce <script>alert("yo")</script> instead of the expected <script>alert("yo")</script>.

Nothing like this could possibly happen if we grab all chars at once and either ways. It's just a fortunate case that after swapping & with & no other replace will be affected, but it's not portable and universally a bad practice.

Grab all chars at once, no excuses!

more details As somebody might think it's an unescape issue only, it's not. Being an anti-pattern with side effects works both ways.

As example, changing the order of the replacement in escaping would produce the unexpected:

function escape(s) {
  return s.replace(/</g, "&lt;")
          .replace(/>/g, "&gt;")
          .replace(/'/g, "&#39;")
          .replace(/"/g, "&quot;")
          .replace(/&/g, "&amp;");
}

escape('<'); // &amp;lt; instead of &lt;

If we do not want to code with the fear that the order wasn't perfect or that our order in either escaping or unescaping is different from the order another method or function used, if we understand the issue and we agree it's potentially a disaster prone approach, if we add the fact in this case creating 4 RegExp objects each time and invoking 4 times .replace trough the String.prototype is also potentially slower than creating one function only holding one object, or holding the function too, we should agree there is not absolutely any valid reason to keep proposing a char-by-char implementation.

We have proofs this approach can fail already so ... why should we risk? Just avoid and grab all chars at once or simply use this tiny utility.

Backtick

Internt explorer < 9 has some backtick issue

For compatibility sake with common server-side HTML entities encoders and decoders, and in order to have the most reliable I/O, this little utility will NOT fix this IE < 9 problem.

It is also important to note that if we create valid HTML and we set attributes at runtime through this utility, backticks in strings cannot possibly affect attribute behaviors.

var img = new Image();
img.src = html.escape(
  'x` `<script>alert(1)</script>"` `'
);
// it won't cause problems even in IE < 9

However, if you use innerHTML and you target IE < 9 then this might be a problem.

Accordingly, if you need more chars and/or backticks to be escaped and unescaped, feel free to use alternatives like lodash or he

Here a bit more of my POV and why I haven't implemented same thing alternatives did. Good news: those are alternatives ;-)