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Short answer

Object types list named properties and their types. Properties may be optional or readonly. You can write them inline or as interfaces/type aliases. [S1][S2]

Points

• Object types can be anonymous. [S1]
• Each property can mark optionality and writability. [S1]
• Everyday Types also shows how to list properties to define an object type. [S2]
• Optional properties are marked with ?. [S2]

Claims

• id: C1 claim: Object types can be written anonymously. source: S1 evidence: "As we've seen, they can be anonymous"
• id: C2 claim: Property types may mark optionality and writability. source: S1 evidence: "the type, whether the property is optional, and whether the property can be written to"
• id: C3 claim: Define an object type by listing properties and types. source: S2 evidence: "To define an object type, we simply list its properties and their types"
• id: C4 claim: Object types can mark properties as optional. source: S2 evidence: "some or all of their properties are optional"

Sources

• [S1] TypeScript: Documentation - Object Types. Microsoft (TypeScript Handbook). https://www.typescriptlang.org/docs/handbook/2/objects.html . License: CC BY 4.0 (microsoft/TypeScript-Website). Accessed 2026-11-05.
• [S2] Everyday Types. TypeScript (Microsoft). https://www.typescriptlang.org/docs/handbook/2/everyday-types.html . License: CC BY 4.0 (microsoft/TypeScript-Website). Accessed 2026-11-05.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

Source notice: TypeScript Handbook / Website docs © Microsoft. Licensed under Creative Commons Attribution 4.0 International (https://github.com/microsoft/TypeScript-Website/blob/v2/LICENSE).

@misc{iil_note_4xbqx434,
  author = {{iinventedlight}},
  title = {{TypeScript object types: inline, interface, or type alias}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/typescript-object-types/},
  note = {Permanent ID iil:note:4xbqx434. License: CC-BY-4.0.},
}

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