Typescript generic object keys By leveraging these types, you can build more robust and adaptable code, ensuring that your functions and classes can handle different object structures while maintaining strict type correctness. So I would like to find a way to have all the keys of a nested object. The KeyValuePair class includes two private generic member variables and a generic function setKeyValue that takes two input arguments of type T and U. Record "Constructs an object type whose property keys are Keys and whose property values are Type. Each of these structures will be covered later in this tutorial, but for now a function will be used as an example to illustrate the basic syntax of generics. interface Dic { [key: string]: Object[] } The typescript literature often refers to this pattern as "the description of an indexable object" with a general form Apr 7, 2016 · Is key-value pair available in TypeScript? If so, how do I do that? Can anyone provide sample, example, or links? Mar 12, 2025 · Key Takeaways TypeScript offers multiple ways to implement dictionaries: index signatures, Record utility, and Map Choose implementation based on your needs: index signatures for simple dictionaries, Record for specific key sets, and Map for advanced features Leverage TypeScript’s type system to ensure compile-time safety for dictionary May 11, 2017 · One thing to note here is, interfaces are enforced types at compile-time, while objects are mostly run-time. TypeScript is a language for application-scale JavaScript development. keys, we bind the generic type variable T to this object. These are the following Sep 5, 2018 · function getNumberFromObject<T>(obj: T, key: keyof T): number { return obj[key] // ERROR: obj[key] might not be a number } I want to specify that key should not only be a key of T, but a key with a number value. Nov 16, 2021 · Generics can appear in functions, types, classes, and interfaces. keys = // all keys of generic Aug 7, 2023 · Have you ever noticed that Object. Jul 23, 2025 · We will look into the effective use of generics in TypeScript to ensure type safety when working with nested objects. We're removing a and b, the keyRemover locks in that first generic, Key. This allows you to create dynamic and strongly-typed objects that adapt to different data structures. Whether you’re a beginner getting started with TypeScript or an experienced developer looking to strengthen your type system, understanding keyof is essential for writing more reliable code. It allows you to define a type that represents the keys of an object without having to manually list them out. To iterate over them is a common task for manipulating or accessing the stored data. (See microsoft/TypeScript#14520 for more information. keys operator. One interesting use case is defining object keys using generics. Edit TypeScript is a language for application-scale JavaScript development. The only way I can think of doing this is Apr 6, 2023 · The keyof operator in TypeScript is used to obtain the union of keys (property names) from a given object type. (Source) As @derek mentioned in another answer, the common denominator of interface and object can be a class that serves both a type and a value. May 23, 2020 · But in TypeScript, an object with all optional properties is a supertype of the same object with any required properties, not a subtype. This shows how generic interfaces provide reusable type definitions. I need to iterate over a large object which is just typed as "object". Jul 18, 2024 · TypeScript's Generic Object Types provide a powerful way to create flexible, reusable, and type-safe object definitions. Feb 6, 2025 · Explore two key strategies for extracting object keys in TypeScript while maintaining type safety. The closest I've gotten is type Keys<T> = { [key in T]: number }, but then when used as follows: Feb 20, 2024 · This article provides a comprehensive guide on creating type-safe dictionaries in TypeScript to enhance code reliability and reduce errors. values (), and Object. 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. It’s useful when you want to work with the property names of an object in a type-safe way, ensuring only valid keys are used. We’ve seen how generics can be used to create flexible components that work over a variety of types while ensuring the integrity of your Dec 21, 2020 · I'm currently attempting to write a higher order function without that will return a new object without the keys passed into the returned function. The looseness of Object. Now, newObject only has c available to it. May 21, 2023 · Playground link In this specific case, since you want all of the properties to have the same type, you could use the built-in generic type Record<Keys, Type> as Aluan Haddad points out rather than writing it explicitly as above. I've been trying to create a type that consists of the keys of type T whose values are strings. This allows us to create an object of KeyValuePair with any type of key and value. Here is the internal definition of the Record type: type Record<K extends string | number | symbol, T> = { [P in K]: T; } In this article, we’ll explore the Record type Jun 8, 2022 · Typescript object keys from generic parameters Asked 3 years, 2 months ago Modified 3 years, 2 months ago Viewed 2k times Jun 25, 2025 · Learn how to loop through objects in TypeScript using forin, Object. keys(x) in TypeScript return the type Array<keyof typeof x>? That's what Object. It’s ideal for data structures to work this way so that they’re re-usable across different data types. In pseudocode it would be keyof T where T[P] is a string. Jan 8, 2023 · 3 Typescript Record Generic Type To Create an object interface with known keys you can use Record, and, to create an object interface with unknown keys you can use [key: string]: TYPE. TypeScript generic object You can define generic objects by using generic interfaces or type aliases. Generics allow you to create components that can work over a variety of types rather than a single one. entries () with clean, type-safe examples. Generic classes have a generic type parameter list in angle brackets (<>) following the name of the class. Here's how the Object. Jan 8, 2024 · Introduction Generics in TypeScript enhance code flexibility and reusability by allowing classes, interfaces, and functions to operate with a variety of types. This guide offers to elucidate the mysteries of generic arrays, delivering ye an ample understanding of their potent capabilities through a cavalcade of code exemplars. Typescript: How to use a generic parameter as object key Asked 6 years, 4 months ago Modified 6 years, 4 months ago Viewed 25k times Oct 30, 2024 · When working with TypeScript, leveraging generics can significantly enhance the type safety and flexibility of your code. Nov 30, 2022 · I want to constrain the key prop to be only keys that are present in T and also where the keys in T are only strings. It is a key-value pair structure, with a fixed type for the keys and a generic type for the values as well. Iterating over object keys in TypeScript can be challenging. Meaning that our conditional can give exact information about the return value. The function will return a new Feb 5, 2025 · Conclusion Generics help preserve types, prevent errors, and improve reusability. TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. Let’s learn how to create and transform object types. Feb 29, 2024 · The type of the name key in the T type is a string and that's the type the get() method should return. keys does, so it seems like an obvious oversight on the part of the TypeScript definition file authors to not make the return type simply be keyof T. It's pretty simple to create a tighter version using generics and keyof operator. Aug 20, 2019 · There's no way to distribute across string, so there's no way to represent in TypeScript the type "an object type with a single key from the set of all possible string literals ". Master TypeScript's generics with exercises from basics to advanced, including conditional types and currying. keyof does something similar but in the typed world only. And since our definition is the most specific of all three keys declarations, TypeScript defaults to using this. One option is casting to keyof typeof to access values, or using type predicates. To see how useful generics are, imagine that you have a JavaScript function that takes two parameters: an object and an array of keys. ts: Mar 25, 2024 · Generic Constraints - A Gentle Introduction to Generics in Typescript In this issue, you will learn about Generic Constraint, it's importance and how to use Generic Constraint in your daily activities as a developer. In this guide, we will explore how to effectively use TypeScript generics as object keys. keys returns a list of an object’s keys. TO Work with Record and for you question : type GenericInputProperties = { value: string; type: HTMLInputTypeAttribute; placeholder: string; min?: number; max Oct 18, 2021 · Ideally, objects of this Keys<T> type would require having a key for every type in T, and couldn't have a key that's not under T. Oct 1, 2024 · In TypeScript, Objects are the fundamental data structures that use key-value pair structures to store the data efficiently. When a user calls with the string "firstNameChanged", TypeScript will try to infer the right type for Key. So, TL;DR, the following piece of code should satisfy the needs: What's going on here is that now we've got Omit, which removes keys from an object. Mar 14, 2023 · That works because we are mapping only the keys of the tuple which are numeric strings, which is what the template literal type `${number}` represents (it's a "pattern" template literal type, as described by microsoft/TypeScript#40598). Nov 27, 2021 · I'm trying to make the key in the interface declaration generic so that if I pass the interface a string, the key will be a string. Generic object types are often some sort of container type that work independently of the type of elements they contain. entries are a little bit tricky to work with in TypeScript? They won't return what you would expect. keys can be a real pain point when using TypeScript. Should I log a bug on their GitHub repo, or just go ahead and send a PR to fix it for them?. Jul 2, 2022 · The first satisfies narrows to T and then the second satisfies narrows to Record<Keys, any> meaning, if its not in the union of Keys it can't exist on the object. keys is defined within Typescript's built-in types, you can find it in lib. This tutorial will delve into creating and using generic classes, helping Aug 20, 2022 · How to have TypeScript generic function with type argument being keyof an object have return type of that object's key's value Asked 3 years, 2 months ago Modified 3 years, 2 months ago Viewed 4k times Here we made on into a generic method. 1) Generic interfaces that describe object properties The following shows how to declare a generic interface that consists of two members key and value with the corresponding types K and V: Oct 20, 2023 · Objects with Dynamic Keys in TypeScript A short little article about TypeScript’s inference system and how we can pre-define custom keys, dynamically This may have duplicates, there may be Aug 27, 2019 · In TypeScript, is it possible to pass each key in an object as a generic to each corresponding value in that object? For instance: interface Items { [key: Key extends string]: Item <Key> Jan 25, 2025 · TypeScript’s keyof operator is a powerful feature that helps ensure type safety when working with object properties. Jan 8, 2024 · Generic type constraints allow you to specify a contract that the generic types must adhere to: function prop<T, K extends keyof T>(obj: T, key: K) { return obj[key]; } Conclusion This tutorial provided a step into the powerful world of TypeScript generics. Dec 14, 2024 · What are Object Key Generics? Object key generics in TypeScript allow you to define a type that represents the keys of an object. Learn when to type the entire object versus focusing solely on keys to write more efficient, maintainable TypeScript code. Objects are the most common data structures in TypeScript. Here's what I mean by 'generic Object type' let myVariable: GenericObject = 1 // Should Oct 12, 2023 · I'm using a variable with a generic as an object key and it doesn't seem to work. Jul 23, 2025 · In TypeScript, we can iterate through the mapped type record with the generic value by extracting the keys and the access its corresponding generic values. Use them when: The function/class should work with multiple types You want TypeScript to infer and enforce types Jan 13, 2025 · A Comprehensive Guide to TypeScript Generics TypeScript generics is a powerful feature that enables developers to write reusable, type-safe components and functions while maintaining flexibility. The above interface constrains the key, but not its value to only strings. By using generics, you can create reusable components that work with a variety of data types without sacrificing type safety. " Apr 10, 2025 · Learn how to write reusable, type-safe code using generic functions, interfaces, classes, and constraints with this comprehensive guide Constructs an object type whose property keys are Keys and whose property values are Type. Pretty cool! Jul 20, 2021 · How to get a list of keys from a generic object type? generic Class: export class GenericExample<T> { private _keys: string []; constructor () { this. I can't see a way to get the key in the reducer t Consider the following typescript enum: enum MyEnum { A, B, C }; If I want another type that is the unioned strings of the keys of that enum, I can do the following: type MyEnumKeysAsStrings = ke Jan 7, 2024 · Introduction In the well-trod land of TypeScript, a versatile creation known as a generic array glimmers with the promise of type safety and flexibility. May 4, 2024 · UppercaseObject<T> maps through all properties of the obj and creates a new object type with all the keys equal to the obj keys and all the values having a string type. Apr 3, 2025 · Generics in TypeScript: A deep dive into the concept of generics, their benefits, and how to use them effectively in your TypeScript projects. So the thing you're looking for is essentially a lower bound generic constraint, but TypeScript doesn't directly support that. It contains an unknown number of objects of the same type. ) Aug 22, 2024 · The TypeScript keyof operator is used to get a union of all keys in an object type. To do that, it will match Key against the content before "Changed" and infer the string "firstName". Feb 27, 2024 · TypeScript, with its powerful type system, offers a feature called Generics, which enables developers to write reusable and type-safe code. Then newObject, when we instantiate the second function, locks in the generic, Obj. Feb 28, 2024 · # Create a Type from an object's Values in TypeScript To create a type from an object's values: Use a const assertion when declaring the object. es5. A mapped type is a generic type which uses a union of PropertyKey s (frequently created via a keyof) to iterate through keys to create a type: This section is all about figuring out how best to represent these generics in terms of the things that are being passed into functions. What are Generics? Hey there, How can I create a generic function type that get object keys as parameters and return a new object ? something like that: const something… Apr 9, 2025 · In TypeScript, the Record type simply allows you to define dictionary-like objects present in languages like Python. This enables you to create generic types that can operate on any object with specific key types. keys always returning a string[] which should return a list of union types of keys. we are going to explore multiple approaches to achieve this. It will return a literal union type listing the "properties" of an object-like type. Mar 22, 2022 · Generic object type with a dynamic key Asked 3 years, 3 months ago Modified 3 years, 3 months ago Viewed 461 times Title says it all - why doesn't Object. This mainly can be done using various approaches like loop, and builtin Object methods. TypeScript is a superset of JavaScript and provides several ways to iterate over object properties. I have a generic type that take a type in parameter. Object. keys (), Object. Oct 20, 2022 · The key of each object should be a key from the Properties generic (keyof Properties) The value of that key will be defined in the Properties (Properties[title] === string) Sep 23, 2022 · If you guys work with Object in Typescript long enough, we all are aware of that one of the most used methods are Object. Here's an example of a generic interface for a key-value pair: interface KeyValuePair<K, V> { key: K; value Jul 23, 2017 · I try to write a generic function which assembles update data for database updates. Mar 5, 2025 · TypeScript ensures the object adheres to this structure, and the output displays the key-value pair as defined. The following code w Aug 15, 2019 · Define prefix for object keys using types in TypeScript Asked 6 years, 3 months ago Modified 2 years, 1 month ago Viewed 22k times Oct 22, 2024 · Let's build a reusable type helper to get all optional keys from an object type in TypeScript. Several techniques can be used to define generic types that match the properties of the objects as listed and explained below. Oct 14, 2023 · Conclusion In TypeScript, conditional types provide a powerful tool for dynamically transforming object keys based on specified conditions. By using object key generics, you can make your code more flexible and reusable across different data structures. Discover best practices, practical examples, and expert tips to elevate your TypeScript skills. Aug 27, 2018 · The idea is to create a simple object which implements the initial interface. Type Guard simply compare the length of arrays - if they have the same length, it means that you provide all properties. May 14, 2025 · Learn how to use TypeScript generics effectively. Use keyof typeof to get a type that represents the object's keys. By employing generics, developers can establish strongly typed keys for nested objects, significantly reducing the likelihood of runtime errors and enhancing code maintainability. Jun 17, 2020 · The moment we pass a concrete object to Object. d. Here's how to properly type them. Jun 17, 2025 · Unlock the power of TypeScript generics for robust, flexible coding. Oct 30, 2024 · Working with Generic Objects When it comes to working with generic objects in TypeScript, you can define interfaces and classes that are parameterized by one or more types. We need this object in order to get its keys length for comparison in the isMyTypeArr Type Guard. This allows you to create flexible and reusable data structures. We can use it to define generic functions that work with any object type, without knowing the specific keys of that type. My goal is to get all the keys of the given type. Here i have a very simple example where I have two objects (I'm using declare to tell TS there's something there wi The keyof operator keyof is Typescript's answer to JavaScript’s Object. Sep 15, 2021 · Is it possible to create a TypeScript type guard function that determines if a given key is in a given (generic) object — very similar to key in obj, but as a functional type guard (required for reasons unrelated to this question). Index the object's type at the specific keys to get a type of its values. Learn how to use them effectively in this comprehensive guide. In older posts I had found solutions using a generator within a cu Aug 5, 2025 · In Typescript, efficiently managing object property types is essential for type safety and code maintainability. keys and Object. Dec 14, 2024 · What are Generic Key-Value Pairs? Generic key-value pairs in TypeScript allow you to define objects where the keys and values can be of any type. This a In this example, genericArrowFunction is a generic arrow function that takes a value of type T and returns the same value. # The solution - K extends keyof T generics We can use a generic on the get method where we specify that generic type K can only be one of the keys of the generic type T which is passed to the class upon initialization. K is erroring: An index signature parameter type must be either ' In typescript is there any way to assign a variable a generic object type. Passed arguments: record to be updated property key a new array item Even though I restrict the key's type using A generic class has a similar shape to a generic interface. This utility can be used to map the properties of a type to another type. The TransformKeys type we've defined in this article allows you to change keys to uppercase, lowercase, capitalize the first letter, or uncapitalize the first letter with ease. lurdaxz fzxn sjcy lkrdtpgm rwvua yxyong lgca pkuqudb ieyrg ltlpow sxsa zgv xbnsedfu obrakfr grako