Typescript interface function type. Interfaces may have optional properties or read-only properties. If this is not a bug in TypeScript, and there is a real reason, then let's come to my second question: I need to specify, that "doSomething" is optional and can either be a function, or a RegExp: Oct 6, 2017 · This is how to declare function types within Typescript interfaces. Interfaces can be used as function types. This guide covers defining and implementing function types in interfaces with practical examples to enhance your TypeScript skills. Quick Reference We have cheat-sheets available for both type and interface, if you want a quick look at the important every-day syntax at a glance. This article on Scaler Topics covers all about Function Interface in TypeScript with examples and explanations, read to know more. Dec 24, 2024 · Learn what interfaces are, how to create them, and how to use them as arguments in TypeScript functions to improve code clarity and maintainability. Summary TypeScript interfaces define contracts in your code and provide explicit names for type-checking. Wrote this article because of confusing information out there and Typescript documentation is not direct about the Sep 5, 2024 · It can be difficult to choose between types and interfaces in TypeScript, but in this post, you'll learn which to use in specific use cases. To describe a function type with an interface, we give the interface a call signature. Interfaces are typically used as class types that make a contract between unrelated classes. What you're doing on the second line is you're defining a function that returns a function. Function Type Expressions The simplest way to describe a function is Mar 15, 2023 · Typescript is capable of defining Interfaces for functions. They’re also values, and just like other values, TypeScript has many ways to describe how functions can be called. Parameter with an Interface Apr 23, 2025 · TypeScript function interfaces define a function's valid parameters and return types. Interface as Type Interface in TypeScript can be used to define a type and also to implement it in the class. In all three examples above, we’ve written functions that take objects that contain the property name (which must be a string) and age (which must be a number). When setting a type to functions, classes, or parameters, an interface is a useful way to define it. They make sure that different functions all accept the same types of parameters and return the same type of data. Feb 6, 2019 · Interfaces help provide that. Jul 28, 2014 · How can I define a return type of void for a function in a Typescript interface? Asked 11 years ago Modified 11 years ago Viewed 35k times Apr 1, 2025 · A TypeScript Interface can include method declarations using arrow functions or normal functions, it can also include properties and return types. Property Modifiers Each property in an object type can specify a couple of things Jun 15, 2017 · The author wanted to define a type for a function that takes a string and returns a boolean. This guide covers syntax, examples, and best practices to enhance your TypeScript coding skills. Let’s learn about how to write types that describe functions. In addition to describing an object with properties, interfaces are also capable of describing function types. Sep 28, 2023 · This in-depth guide covers TypeScript interfaces, their benefits, & code examples of common use cases like typing functions, classes, generics, & more!. The methods can have parameters or remain parameterless. Mar 11, 2025 · One of the most powerful features of TypeScript is interfaces, which allow you to define the structure of objects, enforce consistency, and improve code readability. We will learn how to define an interface for function types and use it. The following interface IEmployee defines a type of a variable. Dec 28, 2024 · Learn how to define and use functions in TypeScript interfaces. Mar 12, 2020 · To me, both interfaces are defining the same, only the notation is different. Dec 27, 2024 · Learn how to use TypeScript interface function properties effectively. What Are Interfaces? An interface in TypeScript is a contract that defines the structure of an object. Functions are the basic building block of any application, whether they’re local functions, imported from another module, or methods on a class.
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