Assert that a variable is not null or undefined

TypeScript uses ! as a non-null assertion operator:

const foo = document.querySelector("#foo"); // Element | null;
const bar = document.querySelector("#bar")!; // Element;

I avoid it because it’s the same as JavaScript’s unary not operator, which makes it difficult to grep. Instead, I generally prefer to assert types with as TypeName.

const foo = document.querySelector("#foo") as Element;

That has a couple drawbacks. Other than being more verbose, it’s possible to cast the type to something incorrect:

const foo = document.querySelector("svg") as HTMLElement;

But! You can chain the ! non-null assertion operator as many times as you want:

const foo = document.querySelector("#foo")!!!; // Element

I prefer that to as assertions. It’s greppable (since using three consecutive unary nots is unlikely), it’s less verbose, there’s no chance of accidentally changing the type and a bunch of repeated exclamation marks definitely calls out that something unusual is happening with that code.