TypeScript Code Review

Includes all guidelines from code-review skill, plus TypeScript-specific rules.

Prefer Strong Types; Avoid Type Inspection on Known Types

The reviewer MUST:

• Avoid runtime type inspection (

  typeof

  ,

  instanceof

  ) when the type is known or enforced by TypeScript.
• Restrict runtime checks to untyped inputs or boundary validation (e.g., API payloads).

Discouraged:

function labelCount(count: number) {
  if (typeof count === "number") return `${count} items`;
  return "n/a";
}

Avoid

any

and

unknown

When Possible

The reviewer MUST:

• Reject

  any

  unless it is a last-resort boundary with clear justification.
• Require immediate narrowing of

  unknown

  with explicit type guards.

The reviewer SHOULD:

• Prefer generics,

  satisfies

  , and well-scoped interfaces over

  any

  .

Type Casting Must Be Justified

The reviewer MUST:

• Require a comment or invariant when using

  as

  , non-null assertions (

  !

  ), or unsafe casts.
• Prefer

  satisfies

  or type guards before asserting a type.

Acceptable with proof:

const payload = parse(input) as Payload; // validated by parse schema

Additional TypeScript Guidelines

The reviewer SHOULD:

• Encourage use of strict TypeScript compiler options
• Prefer

  readonly

  for immutable data
• Use discriminated unions over type assertions
• Prefer

  unknown

  over

  any

  for external data
• Use template literal types where appropriate