strict.md

Setting strict to false makes TypeScript behave in ways which are much less safe.

As an example, strict includes a setting called strictNullChecks. Setting strictNullChecks to false will allow you to assign null to a variable that is supposed to be a string:

let name: string = null; // No error

With strict enabled, TypeScript will, of course, catch this error.

Another example of a strict setting is noImplicitAny. Setting noImplicitAny to false will allow you to leave function parameters un-annotated:

function greet(name) {
  console.log(`Hello, ${name}!`);
}

This can lead to a flood of any types in your codebase - which as we know, leads to a loss of type safety.

In fact, I’ve written this entire book on the premise that you have strict enabled in your codebase. It’s the baseline for all modern TypeScript apps.