@typescript-eslint/no-dynamic-delete

delete sessions[userId] with a key that's only known at run time means you're using the object as a map. TypeScript can't check that the key exists, and delete doesn't tell you whether it removed anything. Use a Map or a Set instead. Their .delete() returns true only if the key was there.

A literal key is fine: a string, a number, or a negative number.

Configure

Off by default. To turn it on:

[lint.rules]
"@typescript-eslint/no-dynamic-delete" = "error" # or "warn"

Examples

Reported:

const sessions: Record<string, Date> = {};

function logout(userId: string) {
  delete sessions[userId];
}

Not reported:

const sessions = new Map<string, Date>();

function logout(userId: string) {
  sessions.delete(userId);
}

const headers: Record<string, string> = {};

delete headers.cookie;
delete headers["set-cookie"];