Angular CLI - Typescript throws: Cannot read property 'length' of undefined

Question

I run in angular 4 project with ng serve and i get error

Cannot read property \'length\' of undefined

but I don\'t have any property length in

Answer 1

My problem was that, for some reason, my envioroment.ts file was missing. So check important files.

Answer 2

I solved this problem (error during refactoring test). All is good for angular v4.3.* and v4.4*

1. Change @angular/cli version 1.7.3 to 1.4.10 in package.json (latest for angular4)
2. rm -rf node_modules
3. npm install --no-optional

Answer 3

You might be missing one or more files that typescript is trying to process. To find out which file you are missing just add

console.log(fileName);

at the starting of the createSourceFile function at node_modules/typescript/lib/typescript.js file.