Unlike classes, an interface is a virtual structure that only exists within the context of TypeScript. No really. For example, Typescript provides primitive data types that can be used for type-check. Lots of time and effort go into creating all our blogs, resources and demos, we'd love if you'd spare a moment to share this one! Hot and shiny React Hooks are just functions used inside functional components. In React applications, just use type aliases. I hope you enjoyed reading! This lets you extend existing JavaScript code without creating a new named type. Types vs Interfaces There are two main tools to declare the shape of an object: interfaces and type aliases. It’s a common convention to prefix interface names with I, so we’ll have a mix of IProps interfaces and Props type aliases in our code. One thing that type aliases can do that interfaces can’t is create an intersection with a type alias that uses union operator within its definition: This can be useful when we want to combine component’s own props with some HOC’s props that might use union operator. Below are the lists of points, describe the key differences between TypeScript Type and Interface: TypeScript Type declaration can introduce a name for any kind of type including primitive, union or intersection type. I’d compose your types through type rather than use declaration merging - but at least you know the main difference(s) now. However, if you are doing some type level trickery with Omit, Pick, extending, intersecting. Intersecting simply means to combine one or more types! Syntax: class { //body } interface … Type aliases and interfaces used to be quite different in their capabilities. HOCs, Redux, pure functions, and a handful of other concepts widely used in React come from a functional world. Interface are also limited - the type alias can be used for more complex types such as tuples, primitives, unions and other more: Let’s talk primitive types. The only job of an interface in TypeScript is to describe a type. So this allows other programs to use the values defined in the files. Here’s how we’d do the same with a type and intersecting the types via &: I’d recommend using a type instead of an interface when you want to intersect types. Functions. First of all, we don’t want to mix interfaces and types. 2. Typescript allows an interface to inherit from multiple interfaces. is because Vue’s Typescript typings internally treat any function passed as a ‘type’ as a function that returns an instance of the interface. Copyright © 2016-2020 Ultimate Courses. Now we’ve explored the various comparisons and recommended approaches, it’s time to talk about Declaration Merging, a feature in TypeScript that applies to just interface and would be a reason to choose an interface over a type. All numbers are stored as floating point numbers. We will look at those next. How to provide a type shape to JavaScript objects. Use the extends keyword to implement inheritance among interfaces. 👋 Hi! Interfaces are the way to type-check custom data types. Type aliases generally have more capability and a more concise syntax than interfaces. Type unions vs. enums # Type unions and enums have some things in common: You can auto-complete member values. TypeScript has two ways of declaring structures of your objects in the form of #types (type aliases) and #interfaces. In this post you will learn how to use the any type in TypeScript, and most importantly - how to use it properly. The syntax for Type can be written as ‘type ABC = {a: number; b: number;}’. Let’s call it “shape” from now on.In TypeScript, an interface is a As we mentioned earlier, type composition is a very useful feature for React applications, and because interfaces cannot be combined with union-based types, at some point we may need to change our interfaces to type aliases. With interfaces, there’s in fact a smarter approach (some might say a bit too clever) called declaration merging. For example, we can build a Vue project with TypeScript b… Owing to the nature of differences between type aliases and interfaces, the decision to use one over another usually depends on your preferred programming style. TypeScript accommodates these two roles by offering various ways of typing arrays. Most of the time a data structure is an array or an object that might contain a few methods. type is for when you need to define a singular something. Interface. I’m honestly not a fan and I feel it could lead to more harm than good. It is defining the contract by which a "thing" must abide by. Todd Motto, author of Exploring JavaScript Array Methods, // { name: string, price: number, getIngredients(): string[] }. Mathew Phillip Wheatley. So there you have it! Interface. Typescript Enums - Deep Dive. Typically we would define a data structure to model a type against our intended variables and function arguments. Second, we won’t be able to just use interfaces either. However, the rational itself seems to predate type composition. Advanced Types. Note, that to achieve this behaviour we have had to create Milkshake, giving us 3 individual type aliases. Yes, strings, numbers etc. Variable Declarations. Here's what you need to know. It’s completely okay to choose a type for your objects and arrays too. This means you need to be super explicit about each type you implement, as it cannot be dynamic or change right now due to TypeScript limitations. The difference between types and interfaces in TypeScript used to be more clear, but with the latest versions of TypeScript, they’re becoming more similar. Personally I don't enforce these a lot on my teams and projects but it does help to have these mentioned as a tiebreaker when someone feels the need to have such strong consistency. Build next generation applications, beginner to master. Here’s my rule: For use cases such as creating new types through things like primitives, union types, and tuple types, I prefer to use the type keyword. Shameless plug: if you want to learn how to use Redux without writing a ton of boilerplate, check my “State management with Rematch” course on Youtube. The main differences between Types and Interfaces in TypeScript. With interfaces, we can re-open previously declared interfaces and add additional properties to it: The code above doesn’t have any errors, because the resulting IUser interface will contain all 3 properties — firstName, lastName, and age. Types vs. interfaces. Ways of typing Arrays # Array role “list”: array type literals vs. interface type Array # An Array type literal consists of the element type … The full documentation of TypeScript can be found here and the full documentation for Flow can be found here. Let’s explore some sensible practices and defaults, whilst uncovering some hidden gems in the TypeScript language and answer the question “Should I use an interface or a type?”. TypeScript is an open-source language which builds on JavaScript, one of the world’s most used tools, by adding static type definitions. What’s the difference between them? Things that you can do in one you can also do with the other with just syntax changes, and of course, there are exceptions. Functional components are generally preferred over class-based components. Typescript support definition file which can hold up type information of existing JavaScript libraries, much like C++ header files which can describe the structure of existing object files? It is not defining the shape of it, it is defining the type of the thing itself. The TypeScript compiler uses interfaces solely for type-checking purposes. To recap, with some personal preferences too, I’d stick with an interface for objects and use the type alias keyword to compose new types on the fly. No spam, just awesome stuff. You’re entering the realms of next level knowledge, woohoo! Hopefully, this article helped you to see the difference between interfaces and type aliases in TypeScript and also convinced you that type aliases are preferable for React applications. If you disagree with any of the points or feel that something is missing, please let me know in the comments. TypeScript Interface is a blueprint which will tell a deriving class what to implement. The typescript compiler is written in Typescript and it compiles to JavaScript. When we compare that to a type - it could easily be confused as an actual object due to the assignment =: This is just my small preference for choosing an interface over using a type here - but you’re free to use the type keyword if you wish. You can only assign a primitive type to a type alias: If you need to use a primitive, use a type. Not only will it create unnecessary clutter, but also increase required mental effort every time we need to think: “Do we have IProps interface or Props type aliases here?”. I'm Todd, creator of Ultimate Courses and Google Developer Expert teaching beginner to advanced JavaScript, Angular, NGRX, TypeScript through my online courses and blogs. TypeScript lets you augment an interface by simply declaring an interface with an identical name and new members. In TypeScript, types and values do not exist on the same Namespace. JavaScript primitive types inside TypeScript. When TypeScript checks the types of the various parts of our program, one of the key approaches it uses is so-called “duck typing”.In other words, we are determining if something can be classified as a particular type by looking at whether or not it has the required characteristics/structure/shape. Master everything JavaScript has to offer. When should we use one over the other? TypeScript: Code must be annotated constantly to get the most out of TypeScript Features. It can only contain the declaration of the members and is responsible for defining the properties, methods, and events. Interface in TypeScript: An Interface in TypeScript is a syntactical obligation that all entities must follow. They are very similar, and for the most common cases act the same. 2. We can achieve a declaration merge by simply declaring the same interface twice in the same scope (this could be either via importing the interface from another module, or declaring it locally next to another interface): Milkshake now contains name, price and getIngredients! TypeScript interfaces and classes define what objects look like and provide type-checking. Interfaces are a no-go here for just a single value as the syntax doesn’t support it. e.g. Supercharge your daily JS development with static types. This is probably because they’re very similar with minor differences. The elements do not necessarily have the same type. TypeScript language extensions to JavaScript. Conclusion. While class and function deal with implementation, interface helps us keep our programs error-free by providing information about the shape of the data we work with. TypeScript: Takes time to compile the code. Type aliases and interfaces are TypeScript language features that often confuse people who try TypeScript for the first time. That means that we’ll also have to rename IProps to Props to avoid further confusion. An interface is extremely helpful when dealing with data structures as they’re a very visual representation (albeit so is type, this is typically my preference). I would like to collect some arguments for the discussion around types vs interfaces. TypeScript has two ways to describe the shape of an object: a type alias and an interface. Once you’re finished, check out my other article on TypeScript Interfaces vs Classes! With TypeScript, VS Code will bug you about it beforehand. This extra work can be avoided by simply using type aliases everywhere. Welcome to this epic TypeScript series on Type Guards. Lets create an object as an interface (recommended approach): Here, I prefer using an interface because it’s clear it’s an interface and not a variable with data assigned - a nice readability win. However, you do it differently: With enums, you get auto-completion after the enum name and a dot. 🙌🏼 Check your email for the download link. Primitives: Type vs Interface. So, interface Foo { n: number; } instead of type Foo = { n: number; }. All Rights Reserved. 1. I understand that in some cases it can be unhelpful to be shown a fully expanded typescript interface. However, it’s no longer true in the latest versions of TypeScript. Interfaces are basically a way to describe data shapes, for example, an object. typescript webdev In one of my recent PRs I changed all interfaces to types because there were already more types than interfaces.In the review, I was asked to revert the change. Enjoy! I find the code is clearer than using extends with intefaces. The “Prop” returns a union type — if an function is passed into it, it will call that function and by typed as the object returned by … The important thing is to be consistent in whichever approach is used so that the code isn’t confusing. TypeScript in 5 minutes. TypeScript: Has an interface which permits to connect with other applications. Time for Coding. Type aliases and interfaces in TypeScript are equivalent in the majority of cases. For the most part, interfaces and types are pretty much the same besides a few differences covered here. With type unions, you get auto-completion in place or – if it’s a union of string literal types – inside string literal quotes. Nevertheless, let’s uncover some more about Types vs Interfaces in TypeScript so you can make a more informed decision. Hopefully, this article helped you to see the difference between interfaces and type aliases in TypeScript and also convinced you that type … How to provide types to functions in JavaScript. 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