Node js + TypeSc + Babel "Error: Cannot find module 'koa'" - node.js

Question

I have cloned a demo . after installing koa,koa-router etc, I got an error. Here is my index.ts file
import Koa from "koa"
import Router from "koa-router"
import logger from "koa-logger"
import json from "koa-json"
const app = new Koa()
const router = new Router()
router.get("/",async(ctx: any,next: any)=>{
ctx.body = {
meg:"Hello world"
}
await next
})
app.use(logger())
app.use(json())
app.use(router.routes()).use(router.allowedMethods())
app.listen(3000,()=>console.log("app is running at 3000"))
Here is my package.json
{
"name": "babel-typescript-sample",
"version": "0.7.2",
"license": "MIT",
"scripts": {
"type-check": "tsc --noEmit",
"type-check:watch": "npm run type-check -- --watch",
"build": "npm run build:types && npm run build:js",
"build:types": "tsc --emitDeclarationOnly",
"build:js": "babel src --out-dir lib --extensions \".ts,.tsx\" --source-maps inline"
},
"devDependencies": {
"#babel/cli": "^7.8.3",
"#babel/core": "^7.8.3",
"#babel/plugin-proposal-class-properties": "^7.8.3",
"#babel/preset-env": "^7.8.3",
"#babel/preset-typescript": "^7.8.3",
"#types/koa": "^2.11.3",
"typescript": "^3.7.5"
},
"dependencies": {
"koa": "^2.11.0",
"koa-bodyparser": "^4.3.0",
"koa-json": "^2.0.2",
"koa-logger": "^3.2.1",
"koa-router": "^8.0.8"
}
}
my file structure loos like:
/-------
-lib
-index.js
-index.d.ts
-node_modules
-src
-index.ts
Actually,before this ,when I run npm run build,I got error src/index.ts:2:20 - error TS2307: Cannot find module 'koa-router'. I write koa-router.d.ts myself, but I don't think it's a great idea, How do you guys resolve?

Answer 1

You have a few options:
Install koa-router typings with npm install --save-dev #types/koa-router.
Set moduleResolution inside tsconfig.json to node. See this for differences. Note that this option only works if the dependency has typings included. In this case, it does not, so first option would be more correct.
Edit paths (points to directory) or types (points to .d.ts) inside tsconfig.json to point to your typings. Yes, writing your typings ("by hand") for existing dependency is generally considered a bad idea, since it could update and therefore break your typings. If a dependency does not have typings, you can contribute to it by generating it using JSDoc, if it uses JavaScript.