TypeScript: Properly Typing Object.keys and Object.entries

2023/08/07

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The article explains that Object.keys and Object.entries can be a little tricky to work with in TypeScript. The author demonstrates that when using Object.keys with a readonly object, it always returns string[], even if the object has specific literal values. This is because TypeScript's types are intentionally open-ended and cannot guarantee the absence of excess properties. To properly type Object.keys, the author suggests using the keyof type operator to capture the possible values of the keys and then casting the result of Object.keys to the desired type. The same approach can be applied to Object.entries. The author also provides an alternative solution using the Entries type from type-fest or creating a generic function. This article is relevant for developers using TypeScript who want to properly type Object.keys and Object.entries.