Directive prologues and JavaScript dark matter (via) Tom MacWright does some archaeology and describes the three different magic comment formats that can affect how JavaScript/TypeScript files are processed:
"a directive";
is a directive prologue, most commonly seen with "use strict";
.
/** @aPragma */
is a pragma for a transpiler, often used for /** @jsx h */
.
//# aMagicComment
is usually used for source maps - //# sourceMappingURL=<url>
- but also just got used by v8 for their new explicit compile hints feature.
Recent articles
- Tips on prompting ChatGPT for UK technology secretary Peter Kyle - 3rd June 2025
- How often do LLMs snitch? Recreating Theo's SnitchBench with LLM - 31st May 2025
- Talking AI and jobs with Natasha Zouves for News Nation - 30th May 2025