Exporting Variables, Functions, and Classes

The export keyword exposes selected declarations from a module, including constants, functions, and classes. The consumer's import names must match named exports. Export the public API, not incidental private helpers.

Reading the code: currency, total and Order become named exports. Calling the exported function computes 36, and the class instance supplies id 9. TypeScript checks the constructor parameter's number type.

Keep the boundary clear: export does not freeze values or make exported classes globally available. Consumers still need an import.

Save the code as exporting-variables-functions-classes.ts. The result below was captured after compiling this exact example with strict TypeScript checking and executing the emitted JavaScript in Node.js.

TypeScript code

export const currency = "USD";
export function total(price: number, qty: number): number { return price * qty; }
export class Order { constructor(readonly id: number) {} }
console.log(`${new Order(9).id}: ${currency} ${total(12, 3)}`);

Verified output

9: USD 36

Build: npx tsc --strict --target es2022 --module commonjs --lib es2022,dom,esnext.disposable exporting-variables-functions-classes.ts; run: node exporting-variables-functions-classes.js. The exact filename may be changed freely. When a multi-file project exists, prefer its tsconfig.json and build scripts.

currency, total and Order become named exports. Calling the exported function computes 36, and the class instance supplies id 9. TypeScript checks the constructor parameter's number type.

The output shown above comes from the initialized values in this program. Replacing a type annotation alone does not transform a JavaScript value.

This separate mini-project demonstrates real imports, exports, or declarations across files. Create each file in one folder, then compile and run main.js. The example was checked separately from the single-file program.

billing.ts

export const unit = "USD";
export function total(p:number,q:number){return p*q;}
export class Bill { constructor(readonly id:number) {} }

main.ts

import {unit,total,Bill} from "./billing"; console.log(new Bill(4).id,unit,total(3,7));

CommonJS setup: compile with npx tsc --strict --target es2022 --module commonjs main.ts and run node main.js. Compile from the same directory so relative modules are discovered. If this example contains helpers.js, keep that runtime file alongside the emitted main.js.

Verified output from the mini-project

4 USD 21

export does not freeze values or make exported classes globally available. Consumers still need an import.

Check both the TypeScript diagnostic and the emitted JavaScript behavior. A program can compile correctly and still need runtime validation or error handling.

Move Order and total to an exported billing.ts file; import both in main.ts.

Before running your change, write down the type you expect TypeScript to infer and the output you expect JavaScript to print. Then check both predictions.

The export keyword exposes selected declarations from a module, including constants, functions, and classes.

Try the practice change and re-run the exact program to test your understanding.