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Severity: error
Category: type-check
Stage: Stage 1

Description

TypeScript intersection types (A & B) are not valid SJS syntax. They allow types to be merged silently, producing shapes that are difficult to reason about and can be unsound.

Use object-type extension (extends) to compose named shapes explicitly.

Example

// ✗ error
type AdminUser = User & { role: string }    // SJS-E005

Fix

// ✓ correct — explicit extension
type AdminUser extends User {
  role: string
}

If the two object types are from separate sources and you cannot extend them, define a new object type that includes both sets of properties explicitly.

Related codes

  • SJS-E008 — conditional types are also banned
  • SJS-E006 — mapped types are also banned
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