Generate TypeScript Enums from Repeated JSON Values

Enums from JSON Data

When a JSON field contains a small set of categorical values, you may prefer a TypeScript enum over a string literal union for its runtime representation and reverse-mapping capabilities.

Example JSON

[
  { "name": "Bug Report", "priority": "high" },
  { "name": "Feature Request", "priority": "medium" },
  { "name": "Documentation", "priority": "low" }
]

Generated TypeScript (enum style)

enum Priority {
  High = "high",
  Medium = "medium",
  Low = "low",
}

interface Ticket {
  name: string;
  priority: Priority;
}

Enum vs String Literal Union

Feature	Enum	String literal union
Runtime value	Yes (compiled to object)	No (erased at compile time)
Reverse mapping	Yes (for numeric enums)	No
Tree-shaking	Partial	Full
Iterable at runtime	Yes (Object.values)	No
Compatibility with plain JS	Requires compilation	Works as-is

When to Choose Enums

• You need to iterate over all possible values at runtime (e.g., populating a dropdown).
• You want to import the enum in both type and value positions.
• Your codebase convention already uses enums.

When to Prefer Unions

• You want the smallest possible bundle (unions are erased by TypeScript).
• You are using as const assertions for similar behavior.
• You need compatibility with plain JavaScript files.

Const Enums

const enum Priority {
  High = "high",
  Medium = "medium",
  Low = "low",
}

const enum is fully inlined at compile time — no runtime object is emitted. However, it is incompatible with --isolatedModules (used by Babel, SWC, and esbuild), so most modern projects avoid it.