Fix jekyll jolt plugin using monkey patching

Written by: Tushar Sharma

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My existing jekyll website started failing with newer jekyll version: 4.4.1. I had to do a monkey patch to resolve this error.

The build started failing

  Liquid Exception: undefined method `=~' for 1:Integer in _posts

The post responsible for the error uses jekyll-jolt.

Monkey Patching

A monkey patch is a technique in dynamic languages (like Ruby) where you modify or extend existing code at runtime without changing the original source files. The name comes from the idea of "monkey-wrenching" your way into existing code—it's a quick and sometimes crude fix.

Key Characteristics

Runtime modification: Changes are applied when the code runs, not during compilation
No source changes: You don't modify the original library files
Permanent for the session: The modifications persist throughout your application's runtime
Global scope: Changes affect all code using that class/module

The Problem

The jekyll-jolt gem has a method called prop? that checks if a string matches a certain pattern. However, it doesn't handle integer values properly—it assumes all input is a string. When an integer is passed, the method crashes because integers don't respond to the regex matching operation.

The Solution: The Monkey Patch

Create a file _plugins/jekyll_jolt_fix.rb. Jekyll automatically loads all .rb files in the _plugins/ directory. When this file loads, Ruby reopens the Jekyll::Tags::TemplateBlock class and replaces the buggy prop? method with our fixed version. From that point forward, any call to prop? uses our improved implementation.