Improve your typing accuracy by enforcing strict null checks

I'm currently looking to enable strict null checks in my TypeScript 2.0 project, but I'm encountering some challenges with the typings of a dependency that is nested within another dependency (referred to as the dependency grandparent).

To provide more context, I am working with dependencies B and C, both of which rely on A. These dependencies are all TypeScript projects that have their code and typings stored in a lib folder, and they have not yet been updated to support strict null checks.

The relevant typings in A are structured as follows:

interface IInterface {
  [key: string]: string;
}

These typings are utilized in both B and C in the following manner:

import { IInterface } from 'A/lib/iinterface';

interface IExtended extends IInterface {
  myOptionalProperty?: string
}

When strict null checks are enabled, the compilation results in the following error messages:

node_modules/B/lib/extended.d.ts(4,3): error TS2411: Property 'myOptionalProperty' of type 'string | undefined' is not assignable to string index type 'string'
node_modules/C/lib/extended.d.ts(4,3): error TS2411: Property 'myOptionalProperty' of type 'string | undefined' is not assignable to string index type 'string'

This leads to a two-pronged question:

  1. In order to meet the requirements of strict checks, the typing in A needs to be adjusted to:

    interface IInterface {
  [key: string]: string | undefined;
}

    I'm uncertain if it's feasible to override such a type, as it's not simply an expansion of existing types. If it is possible, how can this be accomplished?

  2. If feasible, how should this inclusion be implemented to ensure that the typings in B and C are validated against my customized typing, rather than the typings in their respective local node_modules directory?

typescripttypescript-typingstypescript2.0

Answer №1

One way to speed up the compilation process is by instructing the compiler to skip certain library checks for the libraries you are utilizing.
The compiler options now include skipDefaultLibCheck:

Ignore validation checks for user-defined default library (*.d.ts) files.

And skipLibCheck:

Bypass validation checks for the default library (lib.d.ts) file.

By setting this option to true during compilation, you can avoid errors related to the libraries you are using.

For more information, refer to the updates in TypeScript 2:

TypeScript 2.0 introduces a new --skipLibCheck compiler option that allows skipping type checks for declaration files (files with .d.ts extension). This option can significantly reduce compilation times when dealing with large declaration files that are known to be error-free.

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