Video by Hugging Face via YouTube
Transformers.js v4.3 is out, and the big one is structured output.
With the new @huggingface/transformers-structured-output package you can force a model to follow an exact JSON Schema or regex, directly in the browser. No more parsing markdown fences and hoping the model picked the right property names.
In this video I walk through how constrained decoding works, how the new package hooks into the logits processor in Transformers.js, and the technical story behind it: from a WASM wrapper around llguidance to a pure JavaScript implementation with almost no overhead.
Also in 4.3: a complete overhaul of the documentation pipeline and a bunch of community-contributed fixes and features. Thank you!
Chapters
0:00 Transformers.js 4.3 is out
0:26 New documentation pipeline
1:00 Community contributions
1:19 The problem: unreliable JSON from LLMs
2:18 How constrained decoding works
3:25 Adding the structured output processor
3:37 The new packages folder and plugin approach
6:03 Using regex instead of JSON Schema
6:45 Demo: recipe generator
7:33 Behind the feature: llguidance
9:02 Rewriting it in pure JavaScript
9:22 Performance across Gemma 4, Granite and LFM 2.5
10:26 Try it out
Links
Release notes: https://github.com/huggingface/transformers.js/releases/tag/4.3.0
NPM: https://www.npmjs.com/package/@huggingface/transformers/v/4.3.0
Structured output package: https://www.npmjs.com/package/@huggingface/transformers-structured-output