GoKawiilSource Maps: Shipping Features Through Standards
Published on 10 March 2026
Source maps are a vital part of modern web development. Today, we have an official standard, a large group of members, and many exciting features in development! But it wasn't always this way.
It may surprise you to learn that, for years, there was no official standard describing the source map format. On one hand, it is incredible that for 10 years, bundlers, browsers, and devtools worked together with only a shared Google Doc between them! On the other hand, it became impossible to add new features, deprecate old features, and build the necessary devtools to support dozens of deviations.
Why do we need Source Maps? #
Web development used to be simple! You’d write a bit of JavaScript, stick it in a <script> tag, and send it to your users. This also made debugging very simple: the code that ran on the website was the exact code you authored.
As web development became more complex, tools began to emerge to optimize large JavaScript applications. In 2009, Google released Closure Tools, a suite of tools meant to address the growing complexity with applications like Google Maps, Google Docs, and Gmail.
Closure Tools consisted of four discrete tools: an optimizing compiler, a template language, a JavaScript framework, and a developer tool. The compiler would eventually become Google’s Closure Compiler and the developer tool would heavily influence the future of Chrome DevTools.
The compiler and devtools have always gone hand-in-hand, and they form an important relationship that exists to this day. If developers are going to use a compiler to optimize, minify, and alter their source code, they will need devtools that will allow them to map the generated compiler output back to their source code! That is exactly the gap that source maps address.
What’s inside a source map? #
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