Typescript keyof typeof array. Here's my approach for it, I took it from this article TypeScript Utility: keyof nested object and twisted it to support self-referencing types: Using TS > 4. In this chapter, we are going to learn why they are so useful and Mar 15, 2018 · I like this one best as it is clear and explicit in what is being done and valueof nicely complements Typescript's existing keyof and typeof operators. 1 (dunno if it would work with prev versions) Another example of indexing with an arbitrary type is using number to get the type of an array’s elements. Example: export interface IMyTable { id: number; title: string; createdAt: Date; isDeleted: boo Jan 2, 2018 · TypeScript Version: 2. The only way I know to enforce this, for example when a user adds a new key to the object that the key is also added to the array is via something like this. Jul 23, 2025 · The keyof operator is a TypeScript type operator that takes an object type and returns a string or numeric literal union type of its keys. This guide will explore the usage of typeof in TypeScript, demonstrating how it can be used with various data structures such as arrays and objects, and explaining advanced concepts like keyof typeof. keyof extracts all keys from a type as a union of string literals, allowing you to limit keys in generics or function parameters. type ObjValues = valueof<typeof obj>, where obj is an associative array. (The source code is available at the bottom of this article. 3 Would it be possible to have something like the keyof operator for arrays? The operator would be able to access the values in the array. Jan 8, 2025 · This simple trick leverages the keyof and typeof operator to infer the key types of an object at runtime. 5. May 11, 2017 · I've a lot of tables in Lovefield and their respective Interfaces for what columns they have. Dec 20, 2017 · Let's say I have a class: class Test { propA; propB; propC; } I want to create a method that returns an array of strings and type it to be only the keys existing in the Test class, how can The keyof operator takes an object type and produces a string or numeric literal union of its keys. Aug 27, 2018 · I would like to declare a type that requires all the keys of a given type T to be included in an array, e. The type of list in your example gets inferred by the compiler to be Array<{name: string}>, and thus the compiler has completely forgotten the particular string literal types of the name properties by the time you try to define Title. ) Jun 17, 2025 · One of the powerful features in TypeScript is the combination of keyof and typeof operators. May 1, 2020 · I need an array that always contains all the key strings in the given type object. It might come as a surprise, but Tuples are much more interesting than Arrays at the type level. Understanding typeof in TypeScript The Oct 6, 2021 · I have found other similar questions, some about the Keyof Type Operator, with the most relevant being: Get keys of a Typescript interface as array of strings Typescript keyof return array of strings Typescript spread `interface` keys as union of strings In the above questions, however, the result of keyof is only used as a type/value constraint. We can combine this with typeof to conveniently capture the element type of an array literal:. Sep 4, 2024 · When working with TypeScript, leveraging the keyof operator can provide powerful type-checking capabilities. typeof extracts the type of a value or variable so you avoid duplicating type declarations. We can combine this with typeof to conveniently capture the element type of an array literal: Arrays & Tuples After learning about object types in the previous chapter, let's take a look at the second most important data structure of Type-level TypeScript – Tuples. In fact, they are the real arrays of type-level programs. : checkKeys<T>(arr: Array<keyof T>): void { // do something } interface MyType { id: string; value: number; } Currently if a call checkKeys<MyType>, TS will consider the value passed as valid if it contains any key of MyType (id | value): checkKeys<MyType>(['id', 'value']); // valid Nov 27, 2023 · Use the TypeScript keyof operator with features like generics, mapped types, and template literal types to improve type safety in your code. g. As a result, it helps you write safer, more maintainable code and reduces the risk of passing invalid property names. This approach can enhance type safety and improve code maintainability. Another example of indexing with an arbitrary type is using number to get the type of an array’s elements. The following type P is the same type as type P = "x" | "y": In this article, I’ll explain how I implemented this with other features of TypeScript, ‘keyof’ and ‘typeof’. It can even be used with objects rather than types, e. In TypeScript, typeof is a powerful operator that can be used to grab the type of a variable, allowing developers to work with type information dynamically. In simpler terms, it allows you to get a list of the keys of a given object type as a type itself. One interesting use case is creating an array of keyof types to represent a set of keys for a specific type. These operators work together to provide a way to get the keys of an object type at the type level, which is extremely useful for creating type-safe code. ardhn uflf pkexk gcs ghebkx szhd qregk cwza jrbcq swju