code not working by ts-node

[PanditSiddharth]

when i use these commands

tsc test.ts
node test.js

code works

but when i use

ts-node test.ts

it not works why

MyCode

interface String{
  stop(): string;
}

String.prototype["stop"] = function () {
    return this.toLowerCase();
}

console.log("Hi".stop())

[agammann]

Your example works when TypeScript treats the file as a script: the top-level interface String then augments the global String interface. In a module, that declaration is local, so it does not add stop() to the built-in type. A project option such as moduleDetection: "force", or a top-level import/export, can make that difference.

Use an explicit global augmentation so the intent is clear in a module:

export {};

declare global {
  interface String {
    stop(): string;
  }
}

String.prototype.stop = function () {
  return this.toLowerCase();
};

console.log('Hi'.stop());

This printed hi with ts-node 10.9.2 and TypeScript 5.9.3, including with moduleDetection: "force"; the original form failed under that setting. tsc test.ts also does not load your tsconfig.json, while ts-node test.ts normally does, so the two commands can use different settings. npx ts-node --showConfig will show the effective configuration.

Without the actual error/config I cannot say that this is your exact cause, but this removes the script/module ambiguity. TypeScript's global augmentation documentation.