I Built a Text Diff Tool in Pure Vanilla JS — Myers Algorithm from Scratch, 129 Tests, Zero Dependencies

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Learn to build a text diff tool using the Myers algorithm in vanilla JavaScript, with 129 tests and no dependencies, to compare two blocks of text efficiently

intermediate Published 28 Jun 2026
Action Steps
  1. Implement the Myers algorithm in vanilla JavaScript to find the longest common subsequence between two blocks of text
  2. Write 129 tests to ensure the tool is working correctly and efficiently
  3. Use the tool to compare two blocks of text and highlight the differences
  4. Configure the tool to handle different types of text inputs, such as code or plain text
  5. Test the tool with various edge cases, such as empty strings or very large texts
Who Needs to Know This

Developers and software engineers can benefit from this tool to compare and identify changes between different versions of code or text, making it easier to collaborate and track changes

Key Insight

💡 The Myers algorithm is an efficient way to find the longest common subsequence between two blocks of text, making it ideal for building a text diff tool

Share This
📝 Built a text diff tool in pure vanilla JS using Myers algorithm! 129 tests, zero dependencies 🚀 #vanillajs #textdiff #myersalgorithm

Key Takeaways

Learn to build a text diff tool using the Myers algorithm in vanilla JavaScript, with 129 tests and no dependencies, to compare two blocks of text efficiently

Full Article

Every developer ends up needing to compare two blocks of text at some point — a config before and...
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