README.md

TypeScript Tips Everyone Should Know

A curated collection of practical TypeScript patterns that improve safety, readability, maintainability, and developer experience.

Most of these are small individually. Together, they dramatically change how TypeScript code feels to work in.

Table of Contents

1. Prefer unknown Over any
2. Let Type Inference Do the Work
3. Prefer satisfies Over as
4. Derive Types From Values
5. Model Impossible States With Discriminated Unions
6. Use Exhaustive Checks With never
7. Use as const for Constants
8. Use Type Predicates
9. Build Types From Existing Types
10. Validate External Data at Runtime
11. Avoid enum in Most Cases
12. Prefer Inferable Generics
13. Enable Strict Compiler Options
14. Learn Template Literal Types
15. Type Safety ≠ Runtime Safety

Prefer unknown Over any

A lot of type safety starts here.

Most TypeScript problems start when any enters the system.

function parse(data: unknown) {
  if (typeof data === "string") {
    return data.toUpperCase();
  }
}

Why it matters

• Forces validation
• Preserves safety
• Prevents type leakage

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Let Type Inference Do the Work

The best TypeScript code often has fewer explicit types than beginners expect.

const name = "Ada";

Instead of:

const name: string = "Ada";

Over-annotation

• Widens types
• Hurts inference
• Creates maintenance overhead

Inference tends to scale better than annotation.

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Prefer satisfies Over as

One of the most important modern TypeScript features.

const routes = {
  home: "/",
  about: "/about",
} satisfies Record<string, string>;

Instead of:

const routes = {
  home: "/",
  about: "/about",
} as Record<string, string>;

satisfies validates without losing inference.

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Derive Types From Values Instead of Duplicating Them

One of the biggest TypeScript mindset shifts.

const roles = ["admin", "user", "guest"] as const;

type Role = (typeof roles)[number];

Keeping runtime values and types in sync manually almost always drifts over time.

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Model Impossible States With Discriminated Unions

This is where TypeScript starts becoming architectural.

type State =
  | { status: "loading" }
  | { status: "success"; data: User }
  | { status: "error"; error: Error };

These models tend to scale much better than loose optional-property blobs.

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Use Exhaustive Checks With never

Discriminated unions become much more powerful with exhaustiveness checking.

default: {
  const exhaustive: never = state;
  return exhaustive;
}

Future refactors become compiler errors instead of runtime bugs.

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Use as const for Configuration and Constants

Without as const:

const theme = {
  mode: "dark",
};

mode becomes string.

With as const:

const theme = {
  mode: "dark",
} as const;

Now it becomes 'dark'.

Tiny feature, huge usefulness.

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Use Type Predicates for Reusable Narrowing

Connect runtime checks to compile-time intelligence.

function isUser(value: unknown): value is User {
  return typeof value === "object" && value !== null && "id" in value;
}

Then:

if (isUser(data)) {
  data.id;
}

This becomes especially useful around APIs and external input boundaries.

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Build New Types From Existing Types

Think in transformations instead of duplication.

type UserPreview = Pick<User, "id" | "name">;

Learn these utility types

• Pick
• Omit
• Partial
• Required
• Indexed access types

These utilities become much more valuable as applications grow.

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Validate External Data at Runtime

TypeScript does not validate API responses.

This is one of the most misunderstood parts of TypeScript.

const UserSchema = z.object({
  id: z.string(),
  name: z.string(),
});

Type safety ends at runtime boundaries unless you validate.

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Avoid enum in Most Cases

Usually simpler:

const roles = ["admin", "user"] as const;

Than:

enum Role {
  Admin,
  User,
}

In most applications, literal unions end up simpler to refactor, easier to serialize, and less surprising at runtime than enums.

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Prefer Generics That Infer Automatically

Great TypeScript APIs rarely require manual generic arguments.

Less ideal:

getData<User>();

Better:

getData(userSchema);

Inference usually scales better than annotation-heavy APIs.

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Turn On the Strict Compiler Options

Many teams use TypeScript in "autocomplete mode."

Strict mode is where TypeScript really starts paying off.

{
  "strict": true,
  "noUncheckedIndexedAccess": true,
  "exactOptionalPropertyTypes": true
}

These flags dramatically improve correctness.

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Learn Template Literal Types

One of the most powerful modern TypeScript features.

type Route = `/api/${string}`;

Excellent for:

• Routes
• Event names
• CSS utilities
• Design systems
• Query keys

Once you start using them, they show up everywhere.

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"Type-Safe" Does Not Mean "Runtime Safe"

A perfect final tip because it reframes everything.

This compiles:

const user = (await response.json()) as User;

But may still explode at runtime.

TypeScript improves correctness:

• It does not replace validation
• It does not guarantee good architecture
• It does not eliminate runtime bugs

This distinction becomes increasingly important in larger systems.

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