Andrew Gilliland
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TypeScript Tips I Use Every Day

typescript

Prefer type for Object Shapes

Use type for most things - it’s more flexible and composes better with unions and intersections.

type User = {
  id: string;
  name: string;
};

Reserve interface for when you need declaration merging (e.g. extending third-party types).

Use satisfies Instead of Type Assertions

Instead of casting with as, use satisfies to validate a value against a type while preserving the inferred type.

const config = {
  theme: "dark",
  lang: "en",
} satisfies Record<string, string>;

Discriminated Unions

Discriminated unions make state management much cleaner than optional properties:

type Result<T> =
  | { status: "loading" }
  | { status: "success"; data: T }
  | { status: "error"; message: string };

Now TypeScript narrows the type automatically inside a switch or if statement.

as const for Literal Types

const DIRECTIONS = ["north", "south", "east", "west"] as const;
type Direction = (typeof DIRECTIONS)[number];
// "north" | "south" | "east" | "west"

Avoid any, Embrace unknown

When you don’t know the type upfront, use unknown instead of any. It forces you to narrow before using the value, catching bugs at compile time rather than runtime.

These small habits add up to a much more reliable codebase over time.

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