Library cheatsheet

React 19 Cheatsheet

Hooks, components and patterns for React 19 in TypeScript or JavaScript.

Setup

Add state — Keep a value that re-renders the component when it changes.
Update state from the previous value — Pass a function when the new value depends on the old one.
Run an effect — Run code after render, here when the id changes, and clean up before the next run.
Keep a mutable value or DOM node — A ref persists between renders without causing a re-render.
Manage complex state with a reducer — Move state transitions into one function.
Share data without props — Read the nearest value of a context.

Cache a calculation — Recompute only when the dependencies change.
Cache a function — Keep the same function between renders so memoized children don't re-render.
Skip re-rendering a component — Re-render only when the props change.
Keep the UI responsive during an update — Mark a state update as non-urgent.
Load a component on demand — Split code and show a fallback while it loads.

Handle a form action — Track the result and pending state of a form action.
Show an optimistic update — Show the expected result immediately while the request is in flight.
Read a promise or context with use — use can read a promise during render, suspending until it resolves, and can be called conditionally.
Pass a ref as a prop — Function components accept ref as a normal prop, so forwardRef is no longer needed.

Render conditionally — Show content only when a condition is true.
Render a list — Give each item a stable key so React can track it.
Create a controlled input — Keep the input's value in state.
Write a custom hook — Extract reusable stateful logic into a function that starts with use.
Provide a context — Make a value available to every component below the provider.

Hugging Face cheatsheet — The hf command line, and Transformers and Datasets code for downloading, running, training and sharing models.
Matplotlib and seaborn 3 cheatsheet — Draw line, scatter, bar and histogram charts with Matplotlib, and statistical charts with seaborn.
pandas and NumPy 3 cheatsheet — Load, clean, reshape, group and analyze tabular data with pandas, and work with arrays in NumPy.
Polars 2 cheatsheet — Fast DataFrames in Python: expressions, filtering, grouping, joins, lazy queries and file formats.
Prisma ORM cheatsheet — Model your database in a schema, run migrations, and query with the type-safe Prisma Client. Examples use the prisma-client-js generator; check the docs for newer generators.
PyTorch 2 cheatsheet — Tensors, autograd, models, training loops, saving and speed-ups in PyTorch 2.