Procedure for moving a NodeJS project to TypeScript

Question

It seems that just installing it and then changing file extensions to .ts is not enough to effectively move to TypeScript with a NodeJS project. I get about 400 errors that seem to stem mostly from module resolution issues (but not only).

There are a couple of guides covering this topic, but they do not seem to help, maybe because they are one year old at best. Therefor, I want to ask for recent advice.

What steps do I need to take to transition a NodeJS project to Typescript?

Jeff Walden · Accepted Answer · 2024-06-13 05:10:15Z

7

1.Add typings to your devDependencies in package.json

{
  "devDependencies": {
    "typings": "latest"
  },
  "scripts": {
    "postinstall": "typings install --save"
  }
}

2.Add typings.json (alongside your package.json), note postinstall action in the package.json above - this will install typescript definitions upon each npm install

{
  "globalDependencies": {
    "node": "github:DefinitelyTyped/DefinitelyTyped/node/node.d.ts"
  }
}

3.Add tsconfig.json

{ 
     "compilerOptions": { 
         "emitDecoratorMetadata": true, 
         "experimentalDecorators": true,
         "moduleResolution": "node",
         "module": "commonjs", 
         "target": "es6",
         "sourceMap": true,
         "outDir": "dist",
         "declaration": true,
         "allowJs": true,
         "forceConsistentCasingInFileNames": true
     },
     "exclude": [
         "node_modules",
         "dist",
         ".vscode",
         "docs"
     ]
}

Note that allowJs option will help you to keep some javascript files unconverted if necessary.

Make transpiling of ts files part of your build process

This should get you going. After that step by step convert javascript to typescript in order to leverage its benefits.

Hope this helps.

edited Jun 13, 2024 at 5:10

Jeff Walden

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answered Jul 16, 2016 at 19:22

Amid

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7 Comments

Ludwik Over a year ago

Thank you for these detailed steps, it has been hard to know which config options to choose. However, I did try setting allowJs to true to do it incrementally (and add a build directory where the output should go), but then, the ts compiler complained that it cannot compile because it would overwrite the files in the build directory. But I did add the build directory to the excludes, just like node_modules, so I did not know what to do and just changed all files to .ts. Did I miss something there?

Amid Over a year ago

You did not forget to specify outDir in tsconfig? Also this might be connected with how your build is setup, are you using gulp/grunt or compiling directly via tsc. I have used both and both work just fine with allowJs option. I would suggest you to try and reduce your project to minimum in order to clearly see where the problem will disappear.

Ludwik Over a year ago

I did eventually get it to work today morning, by specifying both "exclude" (build, node_modules) and "include" (src, where I moved my code files)(and yes, outDir="build"). This surprised me a lot, but without it (ie. with only "exclude" or "include" I was getting those errors and tsc was setting up the file structure inside build in a very weird way.

Ludwik Over a year ago

Also, with your specific tsconfig.json I get the error TS5053: Option 'allowJs' cannot be specified with option 'declaration'.

Amid Over a year ago

Quite strange, I do use this two options together without any issues. Although you are correct and there is open issue: github.com/Microsoft/TypeScript/issues/7546. Thanks for the info though.

|

basarat · Accepted Answer · 2016-07-17 02:21:57Z

5

Migrating Js to TS

You create a tsconfig.json with allowJs set to true. This allows you to use the .js as it is!. Next you start changing the file extension from .ts to .js one by one, declaring what you find missing as you go along.

I did a video about this about a week ago https://www.youtube.com/watch?v=gmKXXI_ck7w

More :

maybe because they are one year old at best.

I keep this up to date : https://basarat.gitbooks.io/typescript/content/docs/types/migrating.html

Of course if you read it as a book I assume you already have seen the nodejs quickstart : https://basarat.gitbooks.io/typescript/content/docs/quick/nodejs.html

answered Jul 17, 2016 at 2:21

basarat

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3 Comments

Ludwik Over a year ago

Thank you for maintaining that guide. I did try setting allowJs to true to do it incrementally (and add a build directory where the output should go), but then, the ts compiler complained that it cannot compile because it would overwrite the files in the build directory. But I did add the build directory to the excludes, just like node_modules, so I did not know what to do and just changed all files to .ts. Did I miss something there?

basarat Over a year ago

Please also use outDir. This is shown in the video as well :)

Ludwik Over a year ago

I did use it then, but I recently got it working by adding both "include" and "exclude" (and outDir is still there). Weird that I had to use both, but oh well

Krimson · Accepted Answer · 2019-03-29 00:28:17Z

4

There also official documentation on how to do this

https://www.typescriptlang.org/docs/handbook/migrating-from-javascript.html

answered Mar 29, 2019 at 0:28

Krimson

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