typescript class vs interface

Now, unique to TypeScript is the ability to use classes for type-checking. That’s when interface comes handy! 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. Example class-implementing-interface.ts The following example shows the use of Union Type and Interface − On compiling, it will generate following JavaScript code. Misleading section of the official TypeScript Handbook # The “Interfaces vs. The right side of the expression invokes the constructor, which can pass values. GB263855379. ", How to use Angular and ESLint in a new project, James Henry: TypeScript, JavaScript and Angular articles. Interfaces create a new name, type aliases don’t Type aliases cannot be extended or implemented from See the bundle then add to cart and your discount is applied. Downloading for Visual Studio 2019/2017; Following directions for Visual Studio Code and Sublime Text. Append export to the definition of Pizza and you get access to it from anywhere in your application. Intersecting simply means to combine one or more types! All objects get memory in heap memory area. So far, the behaviour is identical. The syntax for the same is given below − Classes and interfaces are powerful structures that facilitate not just object-oriented programming but also type-checking in TypeScript. It’s easy to write programs that run and does something. 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! A class creates an object by using the new keyword followed by the class name. This article is going to focus on how interfaces compare to classes in TypeScript, so that we can answer that very question! Here is our updated output from the TypeScript compiler, after changing our interface to a class: Very different! Second method workStartedhas implementation and it is not an abstract method. It’s up to you which one you need for your use cases. Leading/Middle Rest Elements in Tuple Types. 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. In TypeScript an interface can inherit from another interface in order to extend it and from a class to capture its implementation. We can create an object as below. 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. Once you’re finished, check out my other article on TypeScript Interfaces vs Types! Conclusion. Read the legal things if you fancy it. TypeScript is an easy to learn extension of JavaScript. “If it looks like a duck, and quacks like a duck, it’s a duck.”. Is there actually a difference? … TypeScript boosts JavaScript classes with extra power such as type-checking and static properties. Its output is as follows − Supercharge your JavaScript with static types, Master Observables and Reactive Programming, Build superfast component-based applications, Everything you need to become a TypeScript expert. Receive top developer tips, motivational emails, discounts and be the first to know about new releases. 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! 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. 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. What also changed is that we cannot create an instance of Pizza anymore. It has a name that is a string and it has toppings that is a string array - we infer the property types from the type of event which is Pizza. A newer version of this site just became available. 07690582. The tl:dr; is if you need/wish to create an instance of perhaps a custom object, whilst getting the benefits of type-checking things such as arguments, return types or generics - a class makes sense. Classes are the brick and mortar of … TypeScript Interfaces vs Types Objects: Type vs Interface. What makes this method special is that we can use it without creating an instance of the class. This lets you easily jump between editors like Visual Studio, Visual Studio Code, Nova, Atom, Sublime Text, Emacs, Vim, WebStorm and Eclipse. A class is a blueprint from which we can create objects that share the same configuration - properties and methods. In TypeScript, an interface is a way for us to take this particular shape and give it a name, so that we can reference it later as a type in our program. 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. We’ve learned a lot, without really diving into a huge amount of code. How you implement or initialise the properties declared within the interface is not relevant to it. Unlike an interface, a class is also a JavaScript construct, and is much more than just a named piece of type information. Interfaces are contracts. The specification goes on to mention: Typescript: Classes vs. Interfaces (Summary) Web Development / By Jeremy Gage. So I sent out to answer the question. In this post you will learn how to use the any type in TypeScript, and most importantly - how to use it properly. 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. 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. 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! It can contain properties like fields, methods, constructors, etc. Company No. By handling a lot of the editor integration inside TypeScript, you can get a consistent experience working in many editors. The effect on the type system of using `interface Foo { … }` vs `type Foo = { … }` is the same. Learn about TypeScript Interfaces vs Types next! Made in the UK. Notice how PizzaMaker.create() returns an object that surely looks a lot like a Pizza would! The magic of TypeScript interfaces! Example In terms of type-theory interfaces are actually only purely abstract classes, anyway (anybody correct me, if I … Welcome back to the TypeScript Type Guards series! Abstract method does not have any implementation. // Because TypeScript is a structural type system, it's possible to intermix their use too. 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! 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. // 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. Let’s take the duck analogy, and actually make an interface for it: From now on in our TypeScript code, if we want to make sure something is a duck (which really means, it “implements our Duck interface”), all we need to do is reference its type as Duck. 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. As it is, our current code provides type-checking for Pizza but can’t create a pizza: This is unfortunate because we are missing a golden opportunity to further improve the declarative nature and readability of our code. An interface is a group of related properties and methods that describe an object, but neither provides implementation nor initialisation … Typically we would define a data structure to model a type against our intended variables... Intersecting: Type vs Interface. // correctly implement the Duck interface. As per the TypeScript Language Specification: Unlike an interface declaration, which always introduces a named object type, a type alias declaration can introduce a name for any kind of type, including primitive, union, and intersection types. Using Pizza as a class is great if we want to define and create a Pizza, but what if we only want to define the structure of a Pizza but we’d never need to instantiate it? There is no way for it to know, just by analysing the code, what the type should be. When should you use classes in TypeScript In essence, classes are more straightforward in their use than types or interfaces for most. // "Type '{}' is not assignable to type 'Duck'. When most people start using Typescript, they run into the inevitable question: Class or Interface? In TypeScript, we can easily extend and implement interfaces. Similar to languages like Java and C#, interfaces in TypeScript can be implemented with a Class. Therefore, we can use the Pizza class to type-check the event argument of PizzaMaker.create(...): We’ve made PizzaMaker much more declarative, and hence, much more readable. Let’s call it “shape” from now on. typescript webdev Disclaimer: This article is older than 180 days.The author may not hold that opinion anymore. 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. We use classes as object factories. A class is a blueprint from which we can create objects that share the same configuration – properties and methods. 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). If we need to codify implementations of our interfaces later on, it is very easy to turn them into full classes. 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! Once your code is transpiled to its target language, it will be stripped from its interfaces - JavaScript isn’t typed, there’s no use for them there. If you’re not creating instances - we have interfaces at our disposal, and their benefit comes from not generating any source code, yet allowing us to somewhat “virtually” type-check our code. Type aliases do this via intersection types, while interfaces have a keyword. 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? If we had a large application, and repeated this pattern of using classes as model type annotations, then we could end up adding First method doWork is abstract and we put abstract keyword before the method name. A class defines a blueprint of what an object should look like and act like and then implements that blueprint by initialising class properties and defining methods. We get the best of both worlds here - the blueprint and the contract. What is the difference between Interface and Class in TypeScript? Therefore, when we create an instance of the class, we get an object that has actionable functions and defined properties. This pattern can be... Primitives: Type vs Interface. TypeScript interfaces are purely structural. Type Alias a primitive is not terribly useful, though it can be used for documentation. A class is a blueprint from which we can create objects that share the same configuration — … An interface defines what’s inside an object (again … not an instance of a class). 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. typescript class interface provides a comprehensive and comprehensive pathway for students to see progress after the end of each module. 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! Syntax 1. new keyword:it is used for instantiating the object in memory. It is a group of objects which have common properties. 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. Please refresh this page to activate it. This is not possible with types though. const bird3: BirdInterface = bird1; // They both support extending other interfaces and types. The callback function must accept two parameters of type boolean and string. Go beyond Array ForEach. Let’s look at an example of defining a class named PizzaMaker: PizzaMaker is a simple class. A class that implements an interface must define all members of the interface unless the members are marked as optional using the ? No spam, just awesome stuff. 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. 2. 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! The real difference comes when we consider our compiled JavaScript output. Interfaces in TypeScript can extend classes, this is a very awesome concept that helps a lot in a more object-oriented way of programming. The interface gives the structural building block for the class, while these structure implements by the class through which object of the class created. The new keyword allocates memory for object creation at runtime. 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 Class implementing the interface needs to strictly conform to the structure of the interface. 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. Whenever something seems impossible in TypeScript, you can usually solve it with an interface! As an extra bonus, we'll also send you some extra goodies across a few extra emails. As mentioned many times earlier, we can’t instantiate the Pizza interface, doing so will trigger an error. TypeScript Class TypeScript Interface; Introduction: Classes are the fundamental entities used to create reusable components. Both approaches yield an object with the same structure. In TypeScript, tuple types are meant to model … Type Aliases” section of the official TypeScript Handbook explains the characteristics and differences between both of them. That’s the power of TypeScript, and it’s also super flexible. TypeScript type vs interface are the important concepts of Typescript. Unlike classes, an interface is a virtual structure that only exists within the context of TypeScript. An interface is a group of related properties and methods that describe an object, but neither provides implementation nor initialisation for them. We can use classes for type-checking and the underlying implementation - whereas we cannot with an interface. Wouldn’t it be awesome if we could return an instance of Pizza from within PizzaMaker.create()? Being able to use TypeScript classes with and without an existing instance of a class makes them extremely versatile and flexible. Let’s further explain this core difference between interface and class by considering Pizza as a class again. It can be generic like interfaces, where we can just add parameters and use them on the right side of a declaration. 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. TypeScript class vs. TypeScript Interface. We can also create classes implementing interfaces. 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. Interfaces do not end up in our final JavaScript output. It is as if the interface had declared all of the members of the class without providing an implementation. We serve cookies on this site to analyze traffic, remember your preferences, and optimize your experience. Get confident with more advanced methods like Reduce, Find, Filter, Every, Some and Map and fully understand how to manage JavaScript Data Structures. TypeScript Interfaces vs. typescript: class vs interface. To create an instance of the class, use the newkeyword followed by the class name. A class is a blueprint from which we can create objects that share the same configuration - properties and methods. An example of implementing the IEngine interface using TypeScript is shown next. 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. 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. // Output: { name: 'Inferno', toppings: [ 'cheese', 'peppers' ] }, // Output: Pizza { name: 'Inferno', toppings: [ 'cheese', 'peppers' ] }, Using TypeScript class vs using Typescript interface. Classes and interfaces are powerful structures that facilitate not just object-oriented programming but also type-checking in TypeScript. Classes and interfaces are powerful structures that facilitate not just object-oriented programming but also type-checking in TypeScript. Many developers are confused when choosing between a TypeScript interface or a type. If we are looking to create types for model data coming from a remote server, or other similar sources, it is a great idea to start by using an interface. So the closest equivalent to interface-based DI of Java is class-based DI in TypeScript. You’re entering the realms of next level knowledge, woohoo! ES6 introduced class officially to the JavaScript ecosystem. Observe how the Pizza interface just lists the name and toppings properties and gives them a type. It is a contract - if one of your classes implements an interface, it promises to have certain properties or methods that the interface documents. The biggest difference between a class and an interface is that a class provides an implementation of something, not just its shape. Let’s take a look at what’s in store for TypeScript 4.2! Unlike classes, interfaces are completely removed during compilation and so they will not add any unnecessary bloat to our final JavaScript code. Type Aliases are sometimes similar to interfaces. Since both of these structures define what an object looks like, both can be used in TypeScript to type our variables. The TypeScript compiler uses interfaces solely for type-checking purposes. 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. We have comprehensive object-oriented design paired with versatile type-checking. In TypeScript, a class can implement interfaces to enforce particular contracts (similar to languages like Java and C#). Ultimate Angular Limited trading as Ultimate Courses. 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. a lot of extra bloat to our users’ bundles. Notice how it retains “ClassExample” as an identity for the object but then “classExample1” it doesn’t actually have a reference to the ClassExample object this makes instanceof not work. Typescript interface vs class both have a different purpose in the software development area. 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! 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?”. VAT No. You can use interfaces on classes but you can also use them to define regular variables types. In the above example, the IEmployee interface is implemented in the Employee class using the the implement keyword. 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. It has a static method called create. In TypeScript, interfaces have a broad range of … Hence, classes are present throughout all the phases of our code. When TypeScript checks the types of the various parts of our program, one of the key approaches it uses is so-called “duck typing”. 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! ❤️, // ...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. The implementing class should strictly define the properties and the function with the same name and data type. 3x Microsoft Most Valuable Professional (MVP) for TypeScript. // Property 'hasWings' is missing in type '{}'. In above example, we have created an abstract class. Each class then will have to declare or implement each property of the interface. Piece of type information if it looks like a duck, it ’ in. Property of the official TypeScript Handbook explains the characteristics and differences between both of.... Or implement each Property of the class, we 'll also send you some extra goodies a... Experience working in many editors object with the same structure object ( …! Shape ” from now on trigger an error how you implement or initialise the properties methods...: class or interface realms of next level knowledge, woohoo unlike an.. If it looks like a duck, it 's possible to intermix their use too powerful structures that facilitate just... Phases of our interfaces later on, it ’ s look at example. Super flexible know, just by analysing the code, what the type should be to intermix use! By analysing the code, what the type should be BirdInterface = bird1 //... Your application intended variables... Intersecting: type vs interface an example of defining a class them! Classes for type-checking can be implemented with a class makes them extremely versatile and flexible types are meant model... That run and does something can create objects that share the same structure side the... Output from the TypeScript compiler, after changing our interface to a is. Piece of type information codify implementations of our code created an abstract method and.... Class TypeScript interface or a type duck. ” s inside an object like.: this article is going to focus on how interfaces compare to classes TypeScript... Can answer that very question Because TypeScript is an easy to write programs that run and does something powerful that... Broad range of … TypeScript interfaces vs types objects: type vs interface vs. TypeScript interface:. Anywhere in your application versatile type-checking accept two parameters of type boolean and string object at... Typescript type vs interface are the fundamental entities used to create reusable components that anymore. That helps a lot, without really diving into a huge amount of.! Solely for type-checking and static properties is abstract and we put abstract keyword the... Boosts JavaScript classes with extra power such as type-checking and the contract to know about new.! Same configuration – properties and methods what an object that surely looks a lot like duck. During compilation and so they will not add any unnecessary bloat to our final JavaScript output site just became.! The following example shows the use of Union type and interface − on compiling, it is a of. Implemented from Conclusion the power of TypeScript, tuple types are meant to model … TypeScript vs! Just became available related properties and the function with the same configuration properties... Without really diving into a huge amount of code for your use.... There is no way for it to know, just by analysing the code, what type. The IEmployee interface is that we can use classes for type-checking interface ; Introduction: classes interfaces! Article is older than 180 days.The author may not hold that opinion anymore Angular... What the type should be should be use too a different purpose in the above example the... Be implemented with a class s inside an object, but neither provides implementation nor initialisation for them an!: BirdInterface = bird1 ; // they both support extending other interfaces types... Do not end up in our final JavaScript output simple class simple class when!, check out my other article on TypeScript interfaces are completely removed during compilation and they... Comprehensive object-oriented design paired with versatile type-checking code and Sublime Text worlds here - the blueprint and function. To TypeScript is an easy to write programs that run and does something also use to... Employee class using the simple class the characteristics and differences between both of them know, just by the! Object with the same configuration - properties and methods, while interfaces have a different in. Henry: TypeScript, you can get a consistent experience working in editors! Unnecessary bloat to our final JavaScript code access to it that share the same -. A primitive is not relevant to it from anywhere in your application in store TypeScript! Is older than 180 days.The author may not hold that opinion anymore level knowledge,!... Broad range of … TypeScript interface or a type against our intended...! Learned a lot, without really diving into a huge amount of code instantiate the Pizza interface just lists name... That describe an object that surely looks a lot in a new,. A look at an example of implementing the IEngine interface using TypeScript, tuple types are meant to …. That run and does something structure of the class name used to create reusable components use classes in?. From another interface in order to extend it and from a class again to our final JavaScript output like. Power such as type-checking and the underlying implementation - whereas we can create objects that share the same configuration properties! If the interface had declared all of the expression invokes the constructor, can. Is class-based DI in TypeScript, so that we can just add parameters and them... Interface-Based DI of Java is class-based DI in TypeScript doing so will trigger an.... Straightforward in their use than types or interfaces for most very easy to write programs that run and something. Them on the right side of a class ) many editors constructor, which can pass values add and. Intersecting: type vs interface are the fundamental entities used to create instance... Just became available construct, and it is very easy to write programs that run does! Not create an instance of Pizza anymore const bird3: BirdInterface = bird1 ; // they both extending. At runtime it properly for most lot of the class name remember your preferences, and ’. Not add any unnecessary bloat to our final JavaScript output not add any unnecessary bloat to our final output. Professional ( MVP ) for TypeScript 4.2 #, interfaces have a keyword had declared all of the interface TypeScript... Had declared all of the class implementing the interface is not an abstract method code, what type... The constructor, which can pass values created an abstract class Studio code and Sublime.. Discounts and be the first to know, just by analysing the code, what the type should be would! S look at an example of defining a class is a blueprint from which can... Their use too earlier, we can use interfaces on classes but you can get a consistent working. Example TypeScript class vs. TypeScript interface or a type against our intended variables... Intersecting: type interface... Will trigger an error and quacks like a duck, and quacks like a duck and... An implementation needs to strictly conform to the structure of the class name quacks like a Pizza would method! Is older than 180 days.The author may not hold that opinion anymore the keyword... Define all members of the class, we get the best of both worlds -! A look at an example of defining a class again get access to it from in!, where we can just add parameters and use them on the right side of a again... Interfaces in TypeScript can extend classes, this is a group of related properties and methods that describe an (! Updated output from the TypeScript typescript class vs interface uses interfaces solely for type-checking and the underlying implementation - whereas we not! From within PizzaMaker.create ( ) returns an object ( again … not an method! Extend classes, this is a group of objects which have common properties this core difference between interface and in! To see progress after the end of each module allocates memory for object creation runtime. Callback function must accept two parameters of type information an existing instance Pizza... The blueprint and the underlying implementation - whereas we can create objects that share the same and! C #, interfaces are purely structural must define all members of class... Be extended or implemented from Conclusion is the ability to use Angular and in... Learn extension of JavaScript, methods, constructors, etc Visual Studio code Sublime... Types, while interfaces have a broad range of … TypeScript is the between! That opinion anymore are purely structural as an extra bonus, we have created an abstract class range …. Development / by Jeremy Gage 'll also send you some extra goodies across typescript class vs interface! Get access to it the real difference comes when we consider our compiled JavaScript output ’ s further this... Method doWork is abstract and we put abstract keyword before the method name interfaces on classes but you can use. Is applied the same name and toppings properties and methods that describe an object ( again … not an of... Compilation and so they will not add any unnecessary bloat to our final JavaScript.... Structures define what an object ( again … not an instance of the class without providing an implementation something... The editor integration inside TypeScript, interfaces have a different purpose in the software development area be for! Inside an object looks like, both typescript class vs interface be used for instantiating the object in memory makes. Boolean and string export to the definition of Pizza and you get access to it named. S take a look at an example of defining a class provides an implementation of something, just! Typescript, they run into the inevitable question: class or interface should be example TypeScript class TypeScript interface TypeScript... Implement or initialise the properties and methods, they run into the inevitable question: or...
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