Referencing projects 

The first step in setting up TypeScript 3's multiple projects feature is to reference projects using a new field called references in tsconfig.json. This field is an array of objects that specify projects to reference.

In our working example, let's make ProjectA start to understand the Shared project:

1. Let's change the tsconfig.json in ProjectA to reference the Shared project:

{
  "compilerOptions": {
    ...
  },
  "references": [
    { "path": "../shared" }
  ]
}

"references": [
  { "path": "../shared", "prepend": true }
]

  We're not going to use prepend in our example though.

1. If we compile ProjectA again, a different error is raised:

error TS6306: Referenced project '.../shared' must have setting "composite": true

The error gives a great clue as to what is wrong. We'll resolve this problem with the missing composite setting in the next section.