TypeScript - Strict Null Checks

What is TypeScript

By default in Javascript, the any type can be ... any .. type. In addition, by default, null and undefined are considered to be any types since they cannot be determined by the javascript compiler.

// this produces NO errors.
let basicString: string;

let undefinedType: undefined;
let anyType: any;
let nullType: null;

basicString = undefinedType;
basicString = anyType;
basicString = nullType;

This has lead to countless javascript bugs. You can explicitly prevent this in TypeScript by explicitly setting the compiler option strictNullChecks to true. Then and only then will your variables be protected from being null/undefined/any.

Should you expect the variable you create to have a null value, you can use the Union Types to set it to be either your decided primitive type or null.