如何在TypeScript中正确导出和导入模块

Question

Note: I know there are many posts on this topic, and I've reviewed quite a few already without success (please see my references at the bottom of this post).

I'm trying to run a very simple test in TypeScript, using Visual Studio Code, where I declare a class in one file and import it into another file. However, I continue to run into an issue where the file I am importing into is not recognizing the methods of the class that I exported from the other file.

The exact error messages that I'm receiving at this point are:

[ts] Property 'getFirstName' does not exist on type 'typeof "module-test/src/OtherClass"'.

[ts] Property 'getLastName' does not exist on type 'typeof "module-test/src/OtherClass"'.

I'm using Node 9.3.0 and TypeScript 2.6.2.

Many thanks in advance for any guidance that anyone can offer me!

main.ts

 import * as Other from "./OtherClass"; class myApp { public async start() { console.log("Starting application"); try { let firstName = await Other.getFirstName(); console.log("First Name: " + firstName); let lastName = await Other.getLastName(); console.log("Last Name: " + lastName); } catch (error) { console.error("Unable to get name: " + error) } console.log("Ending application"); } } const app = new myApp(); app.start(); 

OtherClass.ts

 class Other { getFirstName(): string { return "John"; } getLastName(): string { return "Doe"; } } export { Other }; 

Things I've Tried

1. Exporting via the declaration

 export class Other { getFirstName(): string { return "John"; } getLastName(): string { return "Doe"; } } 

2. Exporting the individual functions

 class Other { export function getFirstName(): string { return "John"; } export function getLastName(): string { return "Doe"; } } 

3. Multiple export statements

 module.exports = Other; export { Other }; export * from "OtherClass"; 

4. Multiple import statements

 import * as Other from "./OtherClass"; import { Other } from "./OtherClass"; 

Configuration Files package.json

 { "name": "module-test", "version": "1.0.0", "description": "Simple test of exporting and importing modules", "main": "./lib/main.js", "scripts": { "test": "echo \\"Error: no test specified\\" && exit 1" }, "author": "John Doe", "license": "ISC", "dependencies": { "typescript": "^2.6.2" }, "devDependencies": { "@types/node": "^8.5.2", "@types/typescript": "^2.0.0" } } 

tsconfig.json

 { "compilerOptions": { /* Basic Options */ "target": "es2016", /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', or 'ESNEXT'. */ "module": "commonjs", /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */ "outDir": "./lib/", /* Redirect output structure to the directory. */ "strict": true, /* Enable all strict type-checking options. */ "inlineSourceMap": true, /* Emit a single file with source maps instead of having a separate file. */ "inlineSources": true /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */ } } 

Articles Referenced

• Property 'Server' does not exist on type 'typeof "http"'
• Node.js ES6 how to export class from module?
• Difference between "module.exports" and "exports" in the CommonJs Module System
• how to properly create and import node modules in typescript
• TypeScript - Export and import modules
• https://www.typescriptlang.org/docs/handbook/modules.html

Answer 1

Where to begin? This is many edits away from a valid program; you should probably start with a working example as it's not 100% clear what you want this code to do.

You created a module with a single named export, the class Other .

export { Other };

You then imported the surrounding module object :

import * as Other from "./OtherClass";

In the importing file, the class now has the name Other.Other . But at no point in the code did you actually instantiate the class with new ! So here

let firstName = await Other.getFirstName();

You need to write

const oth = new Other.Other();

This looks silly, of course. Change the import statement (don't have multiple!) to

import { Other } from "./OtherClass";

And now instead you can write

const oth = new Other();

Moving on, we write

let firstName = await oth.getFirstName();

Except that getFirstName isn't an async function, so you should really write

let firstName = oth.getFirstName();