Patterns

Basics shows the language one feature at a time. Patterns shows it doing the work of a real module: running from files, handling failures as values, checking data at the edges, importing other code, and moving a hot loop into WebAssembly.

This section assumes you write JavaScript. If you are new to programming, finish Learn to Program first. It also assumes you have read Basics, or at least Hello TJS, Required vs Optional and Safety & Validation.

The chapters come in six groups, in this order:

• Running code. Running TJS: Files, the CLI and Bundlers comes first, because a real module lives in a file, not in a page. It covers tjs check and tjs run on the command line, importing .tjs files directly under Bun, and adding TJS to a bundled build.
• Functions. Higher-Order Functions and Async Functions show that typed signatures survive what JavaScript programs do all the time: pass functions around, and await them.
• Errors. Safety & Validation showed that a typed function returns an error instead of throwing it, and that a typed function handed that error returns it unchanged without running its body. Error Handling shows how that plays out across a program and where to check. Flight Recorder covers the runtime's error history: a log of every error it saw, including the ones your code ignored.
• Types at runtime. TypeScript's types vanish when it compiles; TJS keeps every function's signature at runtime. Types at Runtime shows how to inspect a signature, validate data against it, and turn it into a JSON Schema (a description of what valid data looks like).
• Imports. Date Formatting, Local Module Imports and Lodash Utilities show TJS using other code: npm packages and your own modules. On these pages a bare import such as 'date-fns' resolves from a CDN, so there is no bundler and no install step; in your own project it resolves through node_modules, and Running TJS covers the build.
• WebAssembly. WebAssembly (WASM) is a low-level format that browsers run at close to native speed. Inline WASM, WASM SIMD, WASM Memory and WASM Functions are a short course in using it from a TJS file: a hot loop in a wasm { } block, then SIMD (one instruction working on four numbers at once), then buffers shared with WASM without copying, then reusable kernels. When WASM is not available, a block runs as JavaScript instead. Skip these until you have measured a loop worth speeding up.

• Running TJS: Files, the CLI and Bundlers
• Higher-Order Functions
• Async Functions
• Error Handling
• Flight Recorder
• Types at Runtime
• Date Formatting (with import)
• Local Module Imports
• Lodash Utilities (with import)
• Inline WASM
• WASM SIMD
• WASM Memory
• WASM Functions (reusable kernels)