TypeChecker

The TypeChecker provides on-demand type checking for TypeScript files in the VFS using heuristic-based analysis. It catches common errors without requiring the full TypeScript compiler.

Quick start

import { boot, TypeChecker } from "@run0/jiki";

const container = boot();
container.writeFile(
  "/src/app.ts",
  `
  const x: any = 42;
  function greet(name) {
    return "Hello " + name;
    console.log("unreachable");
  }
`,
);

const checker = new TypeChecker(container.vfs);
const diagnostics = checker.checkAll("/src");

for (const d of diagnostics) {
  console.log(`${d.file}:${d.line} [${d.severity}] ${d.message}`);
}

API

new TypeChecker(vfs, options?)

checker.check(files)

Check specific files. Returns Diagnostic[] sorted by file and line.

checker.checkAll(dir?)

Discover all .ts/.tsx files in a directory and check them. Default: /src.

Diagnostic

interface Diagnostic {
  file: string;
  line: number;
  column: number;
  message: string;
  severity: "error" | "warning" | "info";
  code?: string;
}

What it detects

• Explicit any usage (when noImplicitAny is enabled)
• Unreachable code after return/throw
• Missing return type annotations on exported functions
• Duplicate variable declarations in the same scope
• Missing files

For full type checking, install TypeScript and run npx tsc --noEmit via the shell.