typescript/no-non-null-assertion Restriction ​
What it does ​
Disallow non-null assertions using the ! postfix operator.
Why is this bad? ​
TypeScript's ! non-null assertion operator asserts to the type system that an expression is non-nullable, as in not null or undefined. Using assertions to tell the type system new information is often a sign that code is not fully type-safe. It's generally better to structure program logic so that TypeScript understands when values may be nullable.
Example ​
ts
x!;
x!.y;
x.y!;