node.js - Why are my typescript interfaces being compiled to javascript? - Stack Overflow

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As I understand it, interfaces are only relevant in Typescript and the tsc piler should be smart enough not to convert them to JS files in the final output. When I pile my code the interfaces are being piled with it. Why is this?

My simplified project structure

src/
  index.ts
  lib/
    EventClient.ts
  interfaces/
    EventClientConfig.ts

What it piles to

dist/
  index.js
  lib/
    EventClient.js
  interfaces/
    EventClientConfig.js

My tsconfig.json

{
  "pilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "outDir": "./dist",
    "lib": ["ES6", "DOM"],
    "target": "ES2018",
    "module": "CommonJS",
    "moduleResolution": "node",
    "esModuleInterop": true,
    "resolveJsonModule": true,
    "baseUrl": ".",
    "removeComments": true,
    "strict": true,
    "typeRoots": ["./node_modules/@types"],
    "rootDir": "./src",
    "types": [
      "node",
      "jest-fetch-mock",
      "express",
      "reflect-metadata"
    ]
  },
  "include": ["src"],
  "exclude": ["dist", "node_modules", "**/*spec.ts"]
}

An interface

export interface EventClientConfig {
  endpoint: string;
  authToken: string;
}

How I'm using the interface

import { EventClientConfig } from '../interfaces/EventClientConfig';

const config: EventClientConfig = {
  endpoint: '/api',
  authToken: '123456'
}

What the interface is piled to

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });

In the piled code EventClient.js makes no actual reference to the EventClientConfig.js so it's definitely not required. Why is Typescript piling the interface files to JS?

As I understand it, interfaces are only relevant in Typescript and the tsc piler should be smart enough not to convert them to JS files in the final output. When I pile my code the interfaces are being piled with it. Why is this?

My simplified project structure

src/
  index.ts
  lib/
    EventClient.ts
  interfaces/
    EventClientConfig.ts

What it piles to

dist/
  index.js
  lib/
    EventClient.js
  interfaces/
    EventClientConfig.js

My tsconfig.json

{
  "pilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "outDir": "./dist",
    "lib": ["ES6", "DOM"],
    "target": "ES2018",
    "module": "CommonJS",
    "moduleResolution": "node",
    "esModuleInterop": true,
    "resolveJsonModule": true,
    "baseUrl": ".",
    "removeComments": true,
    "strict": true,
    "typeRoots": ["./node_modules/@types"],
    "rootDir": "./src",
    "types": [
      "node",
      "jest-fetch-mock",
      "express",
      "reflect-metadata"
    ]
  },
  "include": ["src"],
  "exclude": ["dist", "node_modules", "**/*spec.ts"]
}

An interface

export interface EventClientConfig {
  endpoint: string;
  authToken: string;
}

How I'm using the interface

import { EventClientConfig } from '../interfaces/EventClientConfig';

const config: EventClientConfig = {
  endpoint: '/api',
  authToken: '123456'
}

What the interface is piled to

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });

In the piled code EventClient.js makes no actual reference to the EventClientConfig.js so it's definitely not required. Why is Typescript piling the interface files to JS?

• javascript
• node.js
• typescript
• interface

Share Improve this question Follow asked May 8, 2020 at 14:47 punkrockbuddyhollypunkrockbuddyholly 9,79477 gold badges3939 silver badges7272 bronze badges 3

• 2 If you don't like this behavior you can use a declaration file.d.ts. Also, don't confuse a module with something it exports. – Aluan Haddad Commented May 8, 2020 at 15:01
• 1 @AluanHaddad that solves problem. I renamed all the interface files so that they had a .d.ts suffix and they're no longer in the piled directory. Thanks! – punkrockbuddyholly Commented May 8, 2020 at 15:10
• Glad I could help – Aluan Haddad Commented May 8, 2020 at 15:27

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 6

This was solved thanks to @AluanHaddad who suggested using .d.ts declaration files. I have changed all my interface filenames so that they end with .d.ts and they are no longer included in the output.

The answer to your questions is here modules

In TypeScript, just as in ECMAScript 2015, any file containing a top-level import or export is considered a module. Conversely, a file without any top-level import or export declarations is treated as a script whose contents are available in the global scope (and therefore to modules as well).

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