How to Fix the “Unknown file extension .ts” Error in ts-node
The “Unknown file extension .ts” error occurs in ts-node occurs when "type": "module" is set in your package.json file. To fix it, run the TypeScript file with ts-node --esm my-file.ts, or remove "type": "module" from your package.json file.
For example, in a project with this package.json file:
{
"name": "cb-js",
"version": "1.0.0",
"main": "index.js",
"type": "module",
"license": "MIT",
"devDependencies": {
"prettier": "^2.8.1"
}
}
If you have a TypeScript file in your project, e.g., my-file.ts:
const num: number = 10;
console.log(num ** 2);
Running the ts-node index.ts command will result in the ERR_UNKNOWN_FILE_EXTENSION TypeError:
To fix the “Unknown file extension ‘.ts'” error in ts-node, run ts-node with the --esm option set:
ts-node --esm my-file.ts
# Or
ts-node-esm my-file.ts
# Or
node --loader ts-node/esm my-file.ts
ts-node in esm mode.To avoid using the --esm flag, add the following to your tsconfig.json file:
{
// other settings...
"ts-node": {
"esm": true,
"experimentalSpecifierResolution": "node"
}
}
After doing this, you’ll be able to run the TypeScript file with only ts-node:
ts-node my-file.ts
ts-node.You may also need to add one or more of the following options to your tsconfig.json file:
{
// other settings..
"compilerOptions": {
// other compiler options...
"esModuleInterop": true,
"module": "ESNext", // "module": "CommonJS" should work too
"moduleResolution": "Node"
},
"include": ["/**/*.ts"],
"exclude": ["node_modules"]
}
Remove "type": "module" from tsconfig.json file
Alternatively, instead of doing all of the above, you can simply remove the "type": "module" field from your package.json file.
{
"name": "cb-js",
"version": "1.0.0",
"main": "index.js",
// removed: "type": "module",
"license": "MIT",
"devDependencies": {
"prettier": "^2.8.1"
}
}
And you’ll be able to run the TypeScript file with ts-node successfully.
