object: interfaces and type aliases. Types are preferred more in declaring constants and as return types for functions.

messages. However for publicly exposed TypeScript helps prevents run time errors which would be inevitable in the case of JavaScript for wrongly inferred types. A simple typo in the attribute name will fail the compilation and prevent run-time errors. The differences arise when type keys appear in both types that you want to extend or intersect from. See how TypeScript improves day to day working with JavaScript with minimal additional syntax. Explore how TypeScript extends JavaScript to add more safety and tooling. thread is a good place to start: The following code segments show how this is possible. TLDR: You dont care about each difference? Worked on Web and Mobile apps at Interfaces are preferred when designing an API library or declaring objects. string, number and boolean make up the Primitives in Typescript. type Owl = { nocturnal: true } & BirdType; are that interfaces are open and type aliases are closed. The following code segment shows this. Functions can be annotated with Parameter Types and Return Types. owl = chicken; colourful: false; However, the syntax for extending is different. toys: number; } Although intersect and extend are not 100% the same for interface and type alias, I put them together in this example. const bird1: BirdType = { wings: 2 }; Otherwise the TS compiler spits out an error upon searching an endless recursion. So if the extended or intersected key is not the same type: Here are a few useful applications of this: Typescripts equivalent to OR: The type is either x or y or z or as many as you want. // In the other case a type cannot be changed outside of Both ways can cover similar needs. There are two main tools to declare the shape of an flies: false; Its useful when you add a new field (e.g. This article focuses on the various aspects of Interfaces and Types and when to use them. If you found this post interesting please leave a on this tweet and consider following my journey about #webperf, #buildinpublic and #frontend matters on Twitter. Both Types and Interfaces can extend others, thus supporting the strongly-typed OOP paradigm. }; colourful: true; Specifically, because you will get better error messages when working with interfaces like Chicken. type BirdType = { Yall, let's talk about: type vs interface Ever wondered if you should use type (Type Alias) or interface in Typescript? act the same. interface BirdInterface { interface Chicken extends BirdInterface { its declaration. I put together a quick overview of TS features that you can or can't type with Type Aliases and Interfaces. let chicken: Chicken = { wings: 2, colourful: false, flies: false }; Fluent in Vue, Angular, React and Ionic. For example: Thus to summarize, there are subtle differences to be kept in mind while working with Types and Interfaces in TypeScript. cases around types vs interfaces, this stack overflow This means you can extend an interface by declaring it This can be confusing for anyone working with TypeScriptbeginner or seasoned programmer. For example: Finally, Interfaces in TypeScript support declaration merging, which doesnt work with Type Aliases. it's possible to intermix their use too. TypeScript can give all this support with the help of Interfaces and Types. flies: false; Interfaces and classes in TypeScript act as static blueprints and therefore can not extend type aliases with union operators in the type definition. // One major difference between type aliases vs interfaces chicken = owl; interface Kitten { Passionate about Frontend, tech, web perf &

} see how TypeScript can provide terser and more focused const bird3: BirdInterface = bird1;

TypeScript becomes extremely useful for organizations having large codebases. let owl: Owl = { wings: 2, nocturnal: true }; const bird2: BirdInterface = { wings: 2 }; Proper tools and IDE supporting TypeScript can suggest code completions, detect errors in types, automatically fix errors, and much more. If you also would like to contribute to DelftStack by writing paid articles, you can check the, Write console.log Wrapper for Angular 2 in TypeScript, the Similarities of Interfaces and Types in TypeScript, Differences Between Interfaces and Types in TypeScript, Extend an Interface With Nested Properties in TypeScript. window).

They are very similar, and for the most common cases } I stayed brief and spicy to give the post an overview character. TypeScript is a programming language maintained by Microsoft and is a superset of JavaScript with support for strong typing. A single function call can return an array of values and functions, that are destructured and can be used as fully typed variables: const [name, setName] = useState(''). wings: 2; DelftStack articles are written by software geeks like you. aliases. }; It becomes useful in the case of the production of a public API so that consumers can make further additions to the API by declaring it again. jQuery library for auto completion) onto an existing type (e.g. There are some basic types in TypesSript using Interfaces and Types are constructed.if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[580,400],'delftstack_com-medrectangle-4','ezslot_2',112,'0','0'])};if(typeof __ez_fad_position!='undefined'){__ez_fad_position('div-gpt-ad-delftstack_com-medrectangle-4-0')}; The following code segment shows an example of an interface in TypeScript. type Robin = { nocturnal: false } & BirdInterface; a second time. Type aliases do this via intersection types, while You can add fields to already existing types. One of the best resources for seeing all of the edge type Puppy = { } interface Kitten { What should you use? Now we can implement the same construct with Types. Simon Wicki is a Freelance Developer in Berlin. positive or a negative. Interface vs Type alias in TypeScript 2.7, Type Alias lets you do it but changes that type to, Interface spits an error that the types are not compatible. // Depending on your goals, this difference could be a colour: string; to the recursive property. Recursion are simple to use. In this post youll quickly see what Typescript feature is possible to implement as Type Alias or Interface. }; Make sure you add the optional ? // That said, we recommend you use interfaces over type color: string; purrs: boolean; type Puppy = { Both of the constructs will give the same output. // Because TypeScript is a structural type system, [1/10] pic.twitter.com/2GQwrwnQ0u. interfaces have a keyword. // They both support extending other interfaces and types. Interfaces declared multiple times would merge into one, while multiple declarations of Type Aliases will give errors. https://stackoverflow.com/questions/37233735/typescript-interfaces-vs-types/52682220#52682220, How to provide types to functions in JavaScript, How to provide a type shape to JavaScript objects, How TypeScript infers types based on runtime behavior, How to create and type JavaScript variables, An overview of building a TypeScript web app, All the configuration options for a project, How to provide types to JavaScript ES6 classes, Made with in Redmond, Boston, SF & Dublin. If youve used hooks in react, then you know the usefulness of tuples. types, it's a better call to make them an interface. } wings: 2; JustWatch. interface Peacock extends BirdType { If you hover over the following errors, you can non-fiction books.