@yeger/html-diff

Dependency-free HTML diffing library written in TypeScript.

This is a fork of diff-htmls and html-diff-ts, which are TypeScript ports of HtmlDiff.NET which is itself a C# port of the Ruby implementation, HtmlDiff. This fork drops CJS support to fix various issues in modern ESM projects.

Installation

pnpm i @yeger/html-diff

Project Description

Comparing two HTML blocks, and returns a meshing of the two that includes <ins> and <del> elements. The classes of these elements are ins.diffins for new code, del.diffdel for removed code, and del.diffmod and ins.diffmod for sections of code that have been changed.

For "special tags" (primarily style tags such as <em> and <strong>), ins.mod elements are inserted with the new styles.

API

Options:

• blocksExpression - list of Regular Expressions which will be treated as one block (token) instead of being divided
  • exp - Regular Expression for token itself
  • compareBy - Regular Expression for part of the token by which will be compared made

Usage

Basic

import { diff } from '@yeger/html-diff'

const oldHtml = '<p>Some <em>old</em> html here</p>'
const newHtml = '<p>Some <b>new</b> html goes here</p>'

const result = diff(oldHtml, newHtml)

Result:

<p>
  Some <del><em>old</em></del
  ><ins><b>new</b></ins> html here
</p>

Visualization:

Some
- <em>old</em>
+ <b>new</b>
html here

With blocksExpression

The tokenizer works by running the diff on words, but sometimes this isn't ideal. For example, it may look clunky when a date is edited from 12 Jan 2022 to 14 Feb 2022. It might be neater to treat the diff on the entire date rather than the independent tokens. You can achieve this using AddBlockExpression. Note, the Regex example is not meant to be exhaustive to cover all dates. If text matches the expression, the entire phrase is included as a single token to be compared, and that results in a much neater output.

import { diff } from '@yeger/html-diff'

const oldHtml = '<p>12.11.2022</p>'
const newHtml = '<p>15.12.2022</p>'
const dateRegexp = /\d\d\.\d\d\.\d\d\d\d/g

const result = diff(oldHtml, newHtml, { blocksExpression: [{ exp: dateRegexp }] })

Result:

<p>
    <p><del>12.11.2022</del> <ins>15.12.2022</ins></p>
</p>

Visualization:

<p>
- <em>12.11.2022</em>
+ <b>15.12.2022</b>
</p>

With blocksExpression and compareBy

No diff

import { diff } from '@yeger/html-diff'

// "src" attr is different but "title" - is the same
const oldHtml = '<img src="./old.png" title="title-1" />'
// "src" attr is different but "title" - is the same
const newHtml = '<img src="./new.png" title="title-1" />'

const result = diff(oldHtml, newHtml, {
    blocksExpression: [
      {
        // match <img/> tag
        exp: /<img[\s\S]+?\/>/g,
        // compare only by title="" attribute
        compareBy: /title="[\s\S]+?"/g,
      },
    ],
  })

Result: Will return the new string without comparison to old one - because title attribute is the same

<img src="./new.png" title="title-1" />

Has diff

import { diff } from '@yeger/html-diff'

// "title" attr is different
const oldHtml = '<img src="./old.png" title="old-title" />'
// "title" attr is different
const newHtml = '<img src="./new.png" title="new-title" />'

const result = diff(oldHtml, newHtml, {
    blocksExpression: [
      {
        // match <img/> tag
        exp: /<img[\s\S]+?\/>/g,
        // compare only by title="" attribute
        compareBy: /title="[\s\S]+?"/g,
      },
    ],
  })

Result: Will return the new string with diff to old one - because title attribute has changed

<del>
  <img src="./old.png" title="old-title" />
</del>
<ins>
  <img src="./new.png" title="new-title" />
</ins>

Visualization:

<p>
- <img src="./old.png" title="old-title" />
+ <img src="./new.png" title="new-title" />
</p>