Compiling with tsconfig

A tsconfig.json file tells tsc how to compile your project — which JavaScript version to target, how strict the type checking should be, where compiled files should go — instead of passing a long list of flags on the command line every time.

Creating one

tsc --init

This generates a tsconfig.json in the current directory with sensible defaults, mostly commented out, ready to uncomment and adjust as needed. From then on, running plain tsc with no arguments picks it up automatically and compiles the whole project according to it.

A typical minimal config

{
  "compilerOptions": {
    "target": "ES2020",
    "module": "ESNext",
    "strict": true,
    "outDir": "./dist",
    "rootDir": "./src"
  },
  "include": ["src/**/*.ts"]
}

target sets which JavaScript version the output should run on — older targets add more compatibility shims for newer syntax. outDir and rootDir keep compiled .js files separate from your source .ts files, so tsc reads from src/ and writes to dist/ without mixing the two.

The strict flag

function greet(name) {
  return "Hello, " + name;
}

loose.ts:1:14 - error TS7006: Parameter 'name' implicitly
has an 'any' type.

Without strict, that same function compiles fine, with name silently treated as any. "strict": true is actually shorthand that turns on a whole group of individually-named checks at once — including noImplicitAny, which is what's catching this — rather than a single setting on its own.