ML Without Magic: Building a Tiny Language Model in Pure Node.js and Watching Every Weight Change

Tokenization → embeddings → causal Transformer → LM head → softmax → loss → backpropagation. No TensorFlow, no PyTorch, and no hidden autograd. Repository: tiny-language-model-neuro-js. Most explanations of language models present correct formulas but hide the path between them inside a framework. I wanted the opposite: one small scenario where every scalar is visible and where the terminal clearly shows incorrect answers before learning and correct answers after it. The project now has one command: node src/train.js --generalize --adaptive-teach It requires Node.js 18.19+ and has no dependencies. The result first The model is queried immediately after random initialization: BEFORE TRAINING — random, usually wrong answers > can human read ? model: ? <unk> ... expected: human can read. [WRONG] > can fish swim ? model: ? <unk> ... expected: fish can swim. [WRONG] > can cat read ? model: ? <unk>