Format JSON in TypeScript

Formatting JSON means parsing valid JSON and serializing it again with whitespace and indentation that make the structure easier to read. Parsing first also catches malformed input.

Quick Start#

The following example uses the standard TypeScript API or a widely used package for this task.

Quick start#

1function formatJson(input: string, spaces = ): string {2  const value: unknown = JSON.parse(input);3  return JSON.stringify(value, null, spaces);4}56const formatted = formatJson('{"name":"ToolPorta","active":true}');

Common Operations#

This second pattern covers a common production operation or a safer way to handle real input.

Typed boundary#

1function parseJson(input: string): unknown {2  return JSON.parse(input) as unknown;3}45const value = parseJson(source);6// Validate/narrow `value` before treating it as an application type.

Important Notes#

Do not cast parsed JSON directly to trusted domain types without runtime validation; TypeScript types do not validate external data.

Best Practices#

1. Treat external input as untrusted and handle parse/validation errors explicitly.
2. Keep encoding, units, formats, and library-specific mapping rules explicit at system boundaries.
3. Add test vectors that cover empty input, Unicode text, malformed input, and representative production data.

References#

• RFC 8259: The JSON Data Interchange Format
• TypeScript Handbook