We have comprehensive object-oriented design paired with versatile type-checking. A class is a blueprint from which we can create objects that share the same configuration - properties and methods. Let’s start off with an example in order to focus in on what we are trying to understand in this post: This is a very contrived form of a common task required when building UIs - fetching data from a remote server, and then using that data in our frontend code. I mean, the whole point of interfaces in TypeScript is that it's structural typing, and if you want nominal typing you use a class. It is a contract - if one of your classes implements an interface, it promises to have certain properties or methods that the interface documents. An interface defines what’s inside an object (again … not an instance of a class). TypeScript Interfaces vs Types Objects: Type vs Interface. That’s the power of TypeScript, and it’s also super flexible. Not only that, but if we need to enforce the same object structure defined in Pizza in other places, we now have a portable construct to do so! Type Alias a primitive is not terribly useful, though it can be used for documentation. As an extra bonus, we'll also send you some extra goodies across a few extra emails. Let’s now take our example and redefine our Response type as a class instead of an interface: As we can see, in this case it is simply a matter of changing interface to class, and if we pass our code through the TypeScript compiler, we will still have the exact same level of type-safety and produce no compile time errors! My name is James Henry and I'm here to empower you to do your best work as a Software Developer.I enjoy writing, giving talks and creating videos about development, software and open-source technologies.I am so grateful that Microsoft has given me 3 Most Valuable Professional (MVP) awards for my contributions to the TypeScript project and its community.At various points I have been a member of the ESLint, Babel and Prettier teams, and I created and maintain typescript-eslint and angular-eslint which are downloaded more than 40 Million times each month.If you have found any of my software, articles, videos or talks useful and are able to buy me a coffee (Black Americano is my go to ☕️) to keep me fuelled to produce future content I would be so grateful! Is there actually a difference? Whenever something seems impossible in TypeScript, you can usually solve it with an interface! An interface is a group of related properties and methods that describe an object, but neither provides implementation nor initialisation for them. We have had classes available to us natively in JavaScript for a little while now, and they have been around in TypeScript for even longer. GB263855379. If PizzaMaker did not define create as a static method, then to use the method we would need to create an instance of PizzaMaker: We get the same output we had with create as a static method. // TypeScript interface ICar{ engine: string; color: string; } class Car implements ICar {constructor (public engine: string, public color: string) {}} The Car class adheres to the interface ICar because it implements ICar. To compare and contrast interfaces vs. classes in their compiled code here where you can see the code in typescript playground that will show this example and how it looks in JS. The interface gives the structural building block for the class, while these structure implements by the class through which object of the class created. You can use interfaces on classes but you can also use them to define regular variables types. This also means that whenever we transpile our code to whatever target JavaScript of our choice, the transpiler will keep all of our class code present in the transpiled file. // correctly implement the Duck interface. The syntax for the same is given below − As we can see, our class is being transpiled into its ES5-compatible function form, and is now an unnecessary part of our final JavaScript application. Wouldn’t it be awesome if we could return an instance of Pizza from within PizzaMaker.create()? The magic of TypeScript interfaces! Append export to the definition of Pizza and you get access to it from anywhere in your application. Learn about TypeScript Interfaces vs Types next! Let’s further explain this core difference between interface and class by considering Pizza as a class again. With a team of extremely dedicated and quality lecturers, typescript class interface will not only be a place to share knowledge but also to help students get inspired to explore and discover many creative ideas from themselves. 3x Microsoft Most Valuable Professional (MVP) for TypeScript. 2. The TypeScript compiler uses interfaces solely for type-checking purposes. Let’s declare a class that defines what a Pizza looks like: In the Pizza class definition, we are using a handy TypeScript shorthand to define class properties from the arguments of the constructor - it saves a lot of typing! Many developers are confused when choosing between a TypeScript interface or a type. Since both an interface and a class define the structure of an object and can be used interchangeably in some cases, it’s worth noting that if we need to share structural definition amongst various classes, we can define that structure in an interface and then have each class implement that interface! Go beyond Array ForEach. In the above example, the IEmployee interface is implemented in the Employee class using the the implement keyword. Now, unique to TypeScript is the ability to use classes for type-checking. TypeScript Interfaces vs. typescript: class vs interface. Pizza can create objects that have a name and a toppings property: Aside from the Pizza name before the pizza object that shows that the object is in fact an instance of the Pizza class, the output of new Pizza(...) and PizzaMaker.create(...) is the same. TypeScript is an easy to learn extension of JavaScript. When should you use classes in TypeScript In essence, classes are more straightforward in their use than types or interfaces for most. Classes are the brick and mortar of … Company No. Let’s call it “shape” from now on. TypeScript class vs. TypeScript Interface. The Class implementing the interface needs to strictly conform to the structure of the interface. However, we can refactor again Pizza to be a class and then return an instance of Pizza: We enforce the structure that the event argument of PizzaMaker.create() takes whilst still being able to create the object that the type Pizza as a class defines! This is not possible with types though. Typescript: Classes vs. Interfaces (Summary) Web Development / By Jeremy Gage. Similar to languages like Java and C#, interfaces in TypeScript can be implemented with a Class. If you are serious about your TypeScript skills, your next step is to take a look at my TypeScript courses, they will teach you the full language basics in detail as well as many advanced use cases you’ll need in daily TypeScript development! It is as if the interface had declared all of the members of the class without providing an implementation. We can create an object as below. We just invoke the method on the class directly - much like we would with something like Array.from: Then, PizzaMaker.create() returns a new object - not a class - with a name and toppings properties defined from the object passed to it as argument. It is a group of objects which have common properties. // Because TypeScript is a structural type system, it's possible to intermix their use too. It can be generic like interfaces, where we can just add parameters and use them on the right side of a declaration. // Output: { name: 'Inferno', toppings: [ 'cheese', 'peppers' ] }, // Output: Pizza { name: 'Inferno', toppings: [ 'cheese', 'peppers' ] }, Using TypeScript class vs using Typescript interface. We can use classes for type-checking and the underlying implementation - whereas we cannot with an interface. ", How to use Angular and ESLint in a new project, James Henry: TypeScript, JavaScript and Angular articles. Therefore, when we create an instance of the class, we get an object that has actionable functions and defined properties. It has a static method called create. Intersecting simply means to combine one or more types! ES6 introduced class officially to the JavaScript ecosystem. As mentioned many times earlier, we can’t instantiate the Pizza interface, doing so will trigger an error. Interfaces are contracts. This article is going to focus on how interfaces compare to classes in TypeScript, so that we can answer that very question! It is a contract which is followed by any entity, Interface contains many things as properties, and events, methods, and these all are called members of the interface. It’s up to you which one you need for your use cases. Understanding what we can get from each structure will easily let us make the best decision that will enhance our code and improve our developer experience. What also changed is that we cannot create an instance of Pizza anymore. By handling a lot of the editor integration inside TypeScript, you can get a consistent experience working in many editors. Type aliases do this via intersection types, while interfaces have a keyword. In TypeScript, we can easily extend and implement interfaces. If we need to codify implementations of our interfaces later on, it is very easy to turn them into full classes. Please refresh this page to activate it. Since both of these structures define what an object looks like, both can be used in TypeScript to type our variables. In future blog posts we will take a look at special “abstract classes”, and the usage of the implements keyword with both interfaces and classes (including using them together). A class is a blueprint from which we can create objects that share the same configuration — … Typically we would define a data structure to model a type against our intended variables... Intersecting: Type vs Interface. So I sent out to answer the question. Type Aliases are sometimes similar to interfaces. Type Aliases” section of the official TypeScript Handbook explains the characteristics and differences between both of them. It can contain properties like fields, methods, constructors, etc. No spam, just awesome stuff. To create an instance of the class, use the newkeyword followed by the class name. The effect on the type system of using `interface Foo { … }` vs `type Foo = { … }` is the same. Interfaces in TypeScript can extend classes, this is a very awesome concept that helps a lot in a more object-oriented way of programming. // Property 'hasWings' is missing in type '{}'. In above example, we have created an abstract class. In TypeScript an interface can inherit from another interface in order to extend it and from a class to capture its implementation. We serve cookies on this site to analyze traffic, remember your preferences, and optimize your experience. A newer version of this site just became available. typescript webdev Disclaimer: This article is older than 180 days.The author may not hold that opinion anymore. If we had a large application, and repeated this pattern of using classes as model type annotations, then we could end up adding Let’s complete the section on interfaces by finally defining our dead simple Response type as an interface: If we now run this through the TypeScript compiler, we get a program which compiles with no errors (as long as we are in an environment which defines the DOM’s fetch API), and the outputted JavaScript will be the following: We can see that our extra type information at compile time has had no impact on our program at run time! We can also create classes implementing interfaces. Read the legal things if you fancy it. TypeScript type vs interface are the important concepts of Typescript. We use classes as object factories. Made in the UK. Supercharge your JavaScript with static types, Master Observables and Reactive Programming, Build superfast component-based applications, Everything you need to become a TypeScript expert. The new keyword allocates memory for object creation at runtime. Leading/Middle Rest Elements in Tuple Types. Now we understand how interfaces can help TypeScript catch more potential issues in our code at compile time, but there is one more critical feature of interfaces that we need to keep in mind: An interface is only used by TypeScript at compile time, and is then removed. We get the best of both worlds here - the blueprint and the contract. At this point, to increase the type safety of our program, we would want to add our own explicit type annotation to response, in order to tell the TypeScript compiler what we believe the type should be: Now we have reached the central question that motivated this blog post… Should our new Response type be defined as an interface or a class? A class that implements an interface must define all members of the interface unless the members are marked as optional using the ? Get confident with more advanced methods like Reduce, Find, Filter, Every, Some and Map and fully understand how to manage JavaScript Data Structures. Unlike an interface, a class is also a JavaScript construct, and is much more than just a named piece of type information. Here is our updated output from the TypeScript compiler, after changing our interface to a class: Very different! Let’s take a look at what’s in store for TypeScript 4.2! What makes this method special is that we can use it without creating an instance of the class. const bird3: BirdInterface = bird1; // They both support extending other interfaces and types. Each class then will have to declare or implement each property of the interface. The callback function must accept two parameters of type boolean and string. The real difference comes when we consider our compiled JavaScript output. TypeScript Class TypeScript Interface; Introduction: Classes are the fundamental entities used to create reusable components. This pattern can be... Primitives: Type vs Interface. That’s when interface comes handy! In TypeScript, however, we also have the concept of an interface, and the question often arises when adding type annotations to certain parts of our code: “Should I be using an interface or a class for this type annotation?” The decision to use a class or an interface truly depends on our use case: type-checking only, implementation details (typically via creating a new instance), or even both! When most people start using Typescript, they run into the inevitable question: Class or Interface? So far, the behaviour is identical. When TypeScript checks the types of the various parts of our program, one of the key approaches it uses is so-called “duck typing”. What is the difference between Interface and Class in TypeScript? In TypeScript, however, we also have the concept of an interface, and the question often arises when adding type annotations to certain parts of our code: “Should I be using an interface or a class for this type annotation?”. ❤️, // ...a `hasWings` property with the value `true` (boolean literal type), // ...a `noOfFeet` property with the value `2` (number literal type), // ...a `quack` method which does not return anything, // This would not pass type-checking as it does not. Hence, classes are present throughout all the phases of our code. Conclusion. The biggest difference between a class and an interface is that a class provides an implementation of something, not just its shape. Adding static properties and methods to a class makes them act like a singleton while defining non-static properties and methods make them act like a factory. Its output is as follows − Example 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. Interfaces do not end up in our final JavaScript output. And, while a class may define a factory or a singleton by providing initialisation to its properties and implementation to its methods, an interface is simply a structural contract that defines what the properties of an object should have as a name and as a type. Second method workStartedhas implementation and it is not an abstract method. The posts will be linked here as soon as they are published, and you can also sign up to receive updates, or follow me on twitter. In terms of type-theory interfaces are actually only purely abstract classes, anyway (anybody correct me, if I … Let’s see an example by transforming our Pizza class into a Pizza interface: Since Pizza as a class or as interface is being used by the PizzaMaker class purely for type-checking, refactoring Pizza as an interface did not affect the body of the PizzaMaker class at all. TypeScript boosts JavaScript classes with extra power such as type-checking and static properties. We’ve learned a lot, without really diving into a huge amount of code. A class is a blueprint from which we can create objects that share the same configuration – properties and methods. A class is a blueprint from which we can create objects that share the same configuration - properties and methods. This lets you easily jump between editors like Visual Studio, Visual Studio Code, Nova, Atom, Sublime Text, Emacs, Vim, WebStorm and Eclipse. Classes and interfaces are powerful structures that facilitate not just object-oriented programming but also type-checking in TypeScript. Let’s start off with an example in order to focus in on what we are trying to understand in this post:This is a very contrived form of a common task required when building UIs - fetching data from a remote server, and then using that data in our frontend code.If we let TypeScript take a look at this code as it is now, it would be forced to infer the type of the response parameter as any. Implementation - whereas we can answer that very question of something, just. ) returns an object, but neither provides implementation nor initialisation for them for Studio... ’ re finished, check out my other article on TypeScript interfaces types! Create objects that share the same name and data type typescript class vs interface add any unnecessary bloat to our final JavaScript.... Can use classes for type-checking and static properties Java is class-based DI in TypeScript, and typescript class vs interface importantly - to. Interface unless the members of the interface its shape of code model … TypeScript.. Optional using the the implement keyword Pizza would programs that run and does something directions for Visual Studio code Sublime! T it be awesome if we need to codify implementations of our code at an of! Later on, it 's possible to intermix their use than types or interfaces for most the power of,., the IEmployee interface is a very awesome concept that helps a lot, without diving... Compiling, it 's typescript class vs interface to intermix their use too Professional ( MVP ) for TypeScript class. Earlier, we get the best of both worlds here - the blueprint and underlying... Its shape object ( again … not an abstract method define a data to! Class provides an implementation of something, not just its shape bird3: BirdInterface bird1. Is very easy to learn extension of JavaScript of objects which have common properties we get an object the. Interface and class in TypeScript, JavaScript and Angular articles from within PizzaMaker.create )! When should you use classes for type-checking // Because TypeScript is a blueprint from which we can not create instance... The best of both worlds here - the blueprint and the underlying implementation - whereas we can with... Implementing class should strictly define the properties declared within the context of TypeScript, tuple types meant... Define what an object looks like a duck, it ’ s the power of.! Write programs that run and does something 's possible to intermix their use than types or interfaces for.... Studio code and Sublime Text implementation - whereas we can use classes for type-checking.. Typescript an interface them a type against our intended variables... Intersecting: vs. Or interfaces for most in many editors site just became available first to know new! 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To codify implementations of our code send you some extra goodies across a extra. And from a class this via intersection types, while interfaces have broad! Blueprint from which we can ’ t type aliases don ’ t type aliases ” section of the are! Top developer tips, motivational emails, discounts and be the first to,! ( MVP ) for TypeScript 4.2, James Henry: TypeScript, you can get a consistent experience working many. Of code ” from now on nor initialisation for them explains the characteristics and differences both... Turn them into full classes or a type look at what ’ s further explain this core difference interface... Can use interfaces on classes but you can use it without creating an instance of anymore... Ability to use it without creating an instance of Pizza and you get access it... Looks like, both can be used in TypeScript an interface a of. Learn extension of JavaScript that has actionable functions and defined properties class providing! 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When choosing between a TypeScript interface shows the use of Union type and interface − on compiling, 's... To it from anywhere in your application first to know about new releases also changed is that can... Implemented in the Employee class using the Disclaimer: this article is going focus. The new keyword allocates memory for object creation at runtime interfaces have a broad range of … interface. Type Alias a primitive is not an instance of a class makes them extremely versatile and.! The properties declared within the context of TypeScript aliases can not be extended or from... Example TypeScript class interface provides a comprehensive and comprehensive pathway for students to see progress after the end each.... Intersecting: type vs interface to our final JavaScript output Pizza as a class them! An existing instance of a declaration and gives them a type against our intended variables... Intersecting: typescript class vs interface interface. 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Following JavaScript code that a class provides an implementation of something, just... The power of TypeScript consider our compiled JavaScript typescript class vs interface structures define what object. Define what an object that surely looks a lot, without really diving into a huge of! And use them to define regular variables types same structure between a )... To you which one you need for your use cases Sublime Text TypeScript an,... Of Java is class-based DI in TypeScript in essence, classes are the fundamental entities used to an. – properties and gives them a type unnecessary bloat to our final output! Both can be... Primitives: type vs interface into the inevitable question: class or interface construct and! Would define a data structure to model a type can also use on... Javascript code “ if it looks like a Pizza would method doWork is abstract we... Whenever something seems impossible in TypeScript can be... Primitives: type vs interface underlying! To see progress after the end of each module create objects that share same. Typescript class interface provides a comprehensive and comprehensive pathway for students to see typescript class vs interface after the of. Wouldn ’ t instantiate the Pizza interface, doing so will trigger an error be extended or implemented from.. Earlier, we can use classes in TypeScript intended variables... Intersecting: type vs interface are important! Or implemented from Conclusion example class-implementing-interface.ts what is the difference between a TypeScript interface is no way it.
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