[javascript] How to fix Cannot find module 'typescript' in Angular 4?

I generated Angular 4 app 3 weeks ago using the @angular/cli. After 2 weeks, I tried to run it with the command line ng serve but I am prompted an error below:

Cannot find module 'typescript'
Error: Cannot find module 'typescript'
    at Function.Module._resolveFilename (module.js:469:15)
    at Function.Module._load (module.js:417:25)
    at Module.require (module.js:497:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (C:\Users\mypc\Documents\Angular Projects\my-angular-app\node_modules\@angular\cli\models\config\config.js:5:12)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)

Do you have any idea how to fix this? Thanks.

If you don't have particular needs, I suggest to install Typescript locally.

NPM Installation Method

npm install --global typescript # Global installation
npm install --save-dev typescript # Local installation

Yarn Installation Method

yarn global add typescript # Global installation
yarn add --dev typescript # Local installation

I had the same problem. If you have installed first nodejs by apt and then you use the tar.gz from nodejs.org, you have to delete the folder located in /usr/lib/node_modules.

I had a very similar problem after moving a working project to a new subdirectory on my file system. It turned out I had failed to move the file named .angular-cli.json to the subfolder along with everything else. After noticing that and moving the file into the subdirectory, all was back to normal.

I had a similar problem when I rearranged the folder structure of a project. I tried all the hints given in this thread but none of them worked. After checking further I discovered that I forgot to copy an important hidden file over to the new directory. That was

.angular-cli.json

from the root directory of the @angular/cli project. After I copied that file over all was running as expected.

Run: npm link typescript if you installed globally

But if you have not installed typescript try this command: npm install typescript

For me just running the below command is not enough (though a valid first step):

npm install -g typescript

The following command is what you need (I think deleting node_modules works too, but the below command is quicker)

npm link typescript

If you use yarn instead of npm, you can install typescript package for that workspace by running:

yarn add typescript

or you can install it globally by running:

sudo yarn global add typescript

to be available for any project.

Run 'npm install' it will install all necessary pkg .

If you have cloned your project from git or somewhere then first, you should type npm install.

This should do the trick,

npm install -g typescript