How to Run TypeScript

What you’ll build or solve

You’ll run a TypeScript file from the command line using two common methods. By the end, you’ll be able to run a single file and also run TypeScript directly during development.

When this approach works best

This method works best when:

• You want to run TypeScript scripts locally on your machine.
• You’re building a Node.js project and need a reliable way to execute TypeScript.
• You want quick iteration while coding, without manually compiling every time.

Skip this approach if you’re working in an online editor that already runs TypeScript for you.

Prerequisites

• Node.js installed
• TypeScript installed (global or local)

Check your setup:

node -v

Verify TypeScript:

tsc -v

If TypeScript is installed locally in a project, use:

npx tsc -v

Step-by-step instructions

Step 1: Compile and run with tsc + Node.js

This is the standard way to run TypeScript. TypeScript compiles to JavaScript, then Node runs the JavaScript output.

Create index.ts:

let message: string = "Hello from TypeScript";
console.log(message);

Option A: Compile a single file

If TypeScript is installed globally:

tsc index.ts

If TypeScript is installed locally:

npx tsc index.ts

Now run the output:

node index.js

Option B: Compile an entire project

In a project folder, compile all TypeScript files:

npx tsc

Then run the output file you want with Node, for example:

node index.js

What to look for

• A new .js file appears after compilation.
• If tsc is not recognized, npx tsc should still work inside a project.
• For multi-file projects, a tsconfig.json file helps. You can create one with:

npx tsc --init

Keep that as setup for projects, not a separate running method.

Step 2: Run directly with ts-node (alternative)

Use this method for development when you want to skip manual compilation.

Install ts-node locally:

npm install --save-dev ts-node

Run your file:

npx ts-node index.ts

What to look for

• Your code runs without creating an index.js file.
• If you see module-related errors, you may need a basic tsconfig.json created with:

npx tsc --init

Examples you can copy

Example 1: Quick math script

function add(a: number, b: number): number {
  return a + b;
}

console.log(add(2, 3));

Run via compile + Node:

tsc index.ts
node index.js

Or run directly:

npx ts-node index.ts

Example 2: Read a command-line argument

const name = process.argv[2] ?? "friend";
console.log(`Hi, ${name}!`);

Compile and run:

tsc index.ts
node index.js Sam

Or with ts-node:

npx ts-node index.ts Sam

Example 3: Multiple files with imports

math.ts:

export function multiply(a: number, b: number): number {
  return a * b;
}

index.ts:

import { multiply } from "./math";

console.log(multiply(4, 5));

Compile and run:

npx tsc
node index.js

If imports start getting messy, create a project config:

npx tsc --init

Common mistakes and how to fix them

Mistake 1: Running .ts files with Node

What someone might do:

node index.ts

Why it breaks:

Node does not execute TypeScript.

Correct approach:

tsc index.ts
node index.js

Or run directly:

npx ts-node index.ts

Mistake 2: Forgetting to recompile after changes

What someone might do:

Edit index.ts

Then run:

node index.js

Why it breaks:

Node runs the old compiled file.

Correct approach:

tsc index.ts
node index.js

Or switch to:

npx ts-node index.ts

Mistake 3: Using non-relative imports for local files

What someone might do:

import { multiply } from "math";

Why it breaks:

That looks for a package, not a local file.

Correct approach:

import { multiply } from "./math";

Troubleshooting

If you see tsc: command not found, restart your terminal, or use npx tsc.

If npx tsc compiles but you can’t find output files, check the folder you’re running in and look for .js files next to your .ts files.

If you see permission errors during global installs, use a local install and run npx tsc instead.

If you see Cannot find module './math', confirm the import path starts with ./ and the file name matches exactly.

If you see Cannot use import statement outside a module, create a tsconfig.json with:

npx tsc --init

Then rerun your command.

Quick recap

• Method 1: compile with tsc (or npx tsc), then run with node.
• Method 2: run directly with npx ts-node during development.
• Avoid node index.ts, Node can only run JavaScript.
• Recompile after changes, or use ts-node to skip that step.
• Use npx tsc --init when you need project-level TypeScript settings.