We Analyzed React's Source Code

React is a fascinating codebase. It has evolved over a decade, maintained by some of the best engineers in the world. It is not "clean code" in the academic sense. It is battle-hardened code.

The "Did" Pattern

One of the first things we noticed was the variable naming convention for boolean flags.

let didWarnAboutMaps = false;
let didWarnAboutGenerators = false;
let didWarnAboutStringRefs = {};

An AI, trained on generic tutorials, often defaults to isWarningShown or hasWarned. The React team uses didWarnAbout.... It feels conversational. It feels like a human tracking state in their head.

Intentional Inconsistency

React's source code is full of performance optimizations that break standard "clean code" rules.

// This is a hot path. We avoid the closure allocation.
for (let i = 0; i < children.length; i++) {
  // ...
}

A junior dev (or an AI) might refactor this to children.forEach() or map() because it looks cleaner. The React team knows that in the hot path of the reconciler, every allocation counts. The comment explains the why.

The Verdict

React scores an 89/100 on the Vibe Scale. It is unmistakably human. It is full of history, trade-offs, and pragmatic decisions that an AI simply wouldn't make.