Types vs. interfaces. However, interfaces have a nice syntax for objects, and you might be used to this concept from other languages. With TypeScript, VS Code will bug you about it beforehand. If you are coming from other statically typed languages, this example will help you a lot: This is valid code that will not raise an error. If you need to change the state of an object over time; If you feel this object will need methods to query or mutate its state; When you want to associate behaviors with data more closely; When you need to write the logic that gives functionality to your app. I believe many people might have an itch about this subject, so why not write about it? edit These three data structures can exist in the same plane, although two will not even exist at runtime. Let me know in the comments if anything can be made more explicit! 1. If you were to use types, extending, or merging, you would have to go through the hassle of creating a new type that joins the two. Generally, they do not hold a state nor methods; When you want to express that a value can be of two different types, this is called a union — it should be possible to name this union distinctively (ex: If you are expressing too many associations, you may want to use an. Unlike classes, types do not express functionality or logic inside your application. All the configuration options for a project. Variable Declarations. Historically, interfaces were more powerful which is why a lot of people went with interfaces. A variable kv1 is declared as KeyPair type. From the support perspective, TypeScript is much better because major frontend frameworks like Vue, Angular, and Facebook’s own React all support TypeScript out of the box. You will now have IDE autocompletion, and it will be a lot easier when you come back later to this route to understand what is going on in the req object. TypeScript: Takes time to compile the code. This example is very rudimentary; however, in larger projects where you collaborate with a large team, it’s godsent. 2. To describe a class constructor parameters. It’s best to use types when you want to describe some form of information. The developer experience can be measured using various scenarios, including support by various libraries and frameworks, ease of use, and overall productivity. I wrote the article I wished I had found three years ago. Are good pickups in a bad guitar worth it? They can describe varying shapes of data, ranging from simple constructs like strings, arrays, and objects. How to execute TypeScript file using command line? The interface becomes some sort of contract that must be fulfilled by the classes that implement it. let okay: readonly boolean[]; // works fine However the following declaration is equivalent to readonly boolean[]: Here's a more full fledged example: interface Animal { legs: number; } const cat: Animal = { legs: 4 }; export type feline = typeof cat; feline will be the type Animal, and you can use it as a type wherever you like. Hide or show elements in HTML using display property. Type aliases generally have more capability and a more concise syntax than interfaces. Primitives: Type vs Interface. Imagine that you have an array of animals that can contain two (or more) types of classes. 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. Here's some examples from TypeScript's own code: Interface. Since TypeScript 3.4, there is a difference for the new readonly type modifier. It supports the creation of a new name for a type. I love em’. Two interfaces having the same name get merged. It is divided into three major sections that are Any Type, Built-In Type, and User-Defined Type. In essence, classes are more straightforward in their use than types or interfaces for most. But holds some specific features that will be helpful according to the situation, choosing between them and totally depends on the developer. By using our site, you Now the big difference from “extending” another class is that in the case of Dog Vs. Cat, the internal logic for isDog() is probably different — however, their outcomes are the same. The type checker checks the call to printLabel.The printLabel function has a single parameter that requires that the object passed in has a property called label of type string.Notice that our object actually has more properties than this, but the compiler only checks that at least the ones required are present and match the types required. 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