TypeScript Incremental Strictness

Question

I have a fairly large Typescript project and I'd like to make it more strict. In particular, we have an issue with null-checking in a lot of places so I'd like to use the strict null-checks option. However, there are thousands of errors and its not exactly possible to fix that anytime soon.

But as I'm writing new code, I'd like to be strict with non-nullable types so I'm not piling onto the mess. Is there any way to incrementally improve the strictness of a Typescript project so all new code has strict null checks?

Answer 1

You can use typescript-strict-plugin which allows you to turn on strict mode in specific files or directories.

1. Install the package

npm i -D typescript-strict-plugin

2. Add the plugin to your tsconfig.json

{
  "compilerOptions": {
    //...
    "strict": false,
    "plugins": [
      {
        "name": "typescript-strict-plugin",
      }
    ]
  }
}

3. Mark files you want to strictify with @ts-strict comment

Before:

//no strict comment here
...
const name: string = null; // no error here

After:

//@ts-strict
...
const name: string = null; // TS2322: Type 'null' is not assignable to type 'string'.

Answer 2

I think that the optimal solution is to extend the tsconfig.json with a new one which enables strictNullChecks and which will be used in the IDE.

1. When creating a new functionality there will be strictNullChecks errors in the IDE, it's OK.
2. When refactoring existing code, the appeared strictNullChecks errors will cause you to fix the code. Thus, there will be a gradual migration of the source code to fully enable the strictNullChecks.