Runtime type checks

@di-framework/tsc is a ttsc transform that injects runtime parameter checks from your TypeScript types.

Source stays plain TypeScript — no assert(), schemas, or decorators. On emit, function bodies get typeof/ shape guards synthesized from parameter types.

di-framework init wires this by default (@di-framework/tsc and plugins in tsconfig; ttsc and TypeScript 7+ come with @di-framework/tsc). Use the steps below for an existing app.

Installation

npm i -D @di-framework/tsc

Pulls in ttsc and TypeScript 7+ transitively.

The first build compiles a Go sidecar (cached afterward). Needs a Go toolchain (go 1.26+ recommended; ttsc can pin via TTSC_GO_BINARY).

Setup

tsconfig.json:

{
  "compilerOptions": {
    "strict": true,
    "plugins": [{ "transform": "@di-framework/tsc" }]
  }
}

The package also declares ttsc.plugin for auto-discovery when listed in devDependencies. Explicit plugins[] is recommended so wiring is obvious.

Build with ttsc, not stock tsc:

npx ttsc --emit

Example

interface User {
  id: number;
  name: string;
}

function greet(user: User): string {
  return `hello ${user.name}`;
}

Emitted JavaScript (simplified):

function greet(user) {
  if (typeof user !== "object" || user === null)
    throw new TypeError("Expected user to be an object");
  if (typeof user.id !== "number")
    throw new TypeError("Expected user.id to be a number");
  if (typeof user.name !== "string")
    throw new TypeError("Expected user.name to be a string");
  return `hello ${user.name}`;
}

How it works

ttsc loads the program (parse + typecheck).
The plugin walks FunctionDeclaration nodes.
For each required parameter, it reads the type (syntax keywords, else checker).
It synthesizes if/throw AST nodes and prepends them to the body.
Emit prints JavaScript from the mutated AST.

Limitations

Skipped today:

methods, arrow functions, function expressions
optional / default / rest / destructured parameters
unions, arrays, tuples, classes, branded types, typia-style tags

Monorepo note

@di-framework/tsc is isolated from the monorepo’s TypeScript 5.x tsc graph (package build is a no-op). ttsc and TypeScript 7+ are dependencies of @di-framework/tsc (kept out of root / other @di-framework/* packages).

Next Steps

CLI - App init/check/build and maintainer mx
Installation - Core package setup
Best Practices - Recommended patterns

Last modified: 09 August 2026