Correct type definition for a variable assigned with an enum. And we re-configured typegeneration to emit the unions for GQL enums. Or did you start at 0 so that the values double as indices over an array of localized strings? Union types appear to offer a more concise, readable list of values than TypeScript enums do! More portable, you still get auto-complete and they are compiled away from the code into types only, without ever reaching the JavaScript output. I am used to see values that are constants as ALL_CAPITALIZED and the usage of Enums seems more straightforward. TypeScript provides both numeric and string-based enums. With you every step of your journey. The visible() function takes an argument of type Roles, which is the enumeration we defined. But since they come with their own pitfalls, it's also not a solution for everybody. If you dont care about the values are are using the enum to represent a set of In TypeScript, similarly to any other language, enum variants can be assigned to a number or a string value. While it's true that this detail is fixed if you use a constant enum, but I've been on multiple projects and seen people using regular enums everywhere and wonder why their output is so big. For example, you can write an if statement that checks whether the userRole is greater than or equal to Role.Admin. Once unpublished, all posts by ishanbagchi will become hidden and only accessible to themselves. If ivanzm123 is not suspended, they can still re-publish their posts from their dashboard. We do have to be careful with using enums this way, though. infer the same type if we use the Array.find method to resolve a value from Now it is clear what values are valid for this enum as weve done that explicitly. But why is that? How to Filter Unique values in CloudWatch Insights (+ 3 other query snippets), Clever coding tricks ( that we don't need ), an absent-minded developer might assign somewhere a different value ( using the assign operator instead of the comparison). DEV Community A constructive and inclusive social network for software developers. In your database you may have this value stored as a number but by defining it as a TypeScript enum we can cast it properly: This explicit cast thats being done during assignment will turn the day variable from a number to our enum, meaning that we can get a bit more of an understanding of what it represents when its being passed around our codebase. In my opinion, this is the most credible argument against TypeScript native enums - basic data manipulation is a common operation on lists, and the transpilation issue above is an easy source of bugs and confusion. Productivity obsessed, avid learner in the paragraph above, you write how bad it is that the typescript does not check that the value is in the range of the Enum. Demands FruitStringEnum.APPLE, // Cannot specify that function only takes Fruits.APPLE, // Cannot pass Fruits.APPLE instead of "APPLE", "If the type is shaped like a duck, it's a duck", There is certainty that the enum values do not require any object manipulation, There is no need for type safety over specific enum members. The issue with TypeScript enums is that they aren't a great fit for JavaScript and were largely inspired by C# enumerations. We would ideally want to type it in a way that is backwards compatible with usage as a string and can also be used as a choice between some pre-defined options. I prefer unions. However, we also cant pass in an arbitrary string, since the enum knows what string values are valid. But things may not always be as they seem, what do you think you get if you pass this through the TypeScript compiler? They allow developers to express intent and enforce type safety, preventing the use of invalid values. Ill point out where the trouble with enums can be particularly pervasive and In this blog, we will debunk the myths surrounding TypeScript Enums and explore their benefits and best practices. If dvddpl is not suspended, they can still re-publish their posts from their dashboard. a set of options selectable by the user. If this was a value coming from a data source of some sort, we have some ambiguity in our application. I consider it preferable to transmitting arbitrary strings or ints. Avoid tightly coupling business logic with enum values that might change frequently. Depending on the use case, enums go really quickly from useful to bad, to ugly. Because types are not compiled to javascript. Regular numeric enums, such as in an enum where you don't set string values, are not type safe! The only cases where string enums may be counter-productive could be when: In the case where the team includes inexperienced developers, using string enums may elevate the risk of the accidental usage of harmful enum variants such as numeric and non-string TypeScript enums. And if someone now thinks, counting down the days of the week is trivial, tell me: what's the first value in your enum? In short, using objects or types instead of ENUMs is a better option in terms of flexibility, scalability, clarity, readability, and security. Once unpublished, this post will become invisible to the public and only accessible to Ivan Zaldivar. Privacy Policy. DEV Community A constructive and inclusive social network for software developers. For more information, please see our In particular, it can If like in our above example you need both the type and the associated Yet personally the strange syntax of POJOS (const as const) is less readable and may be confusing for newer developers. However, there have been debates about whether TypeScript Enums are good or bad. Enum is not defined. At the very least, it is something to learn once and not have to think about again. Enums are a new data type supported in TypeScript. Its a group of named constant values that you can use within your code. Recently in our projects we started using Typescript and among many features we extensively adopted, there are Enums. Types are also flexible and scalable, and also offer better code clarity and readability. Another problem with regular numeric enums that do not set string values is that they are not type-safe. Consider Future Changes: Anticipate potential changes to enum values and design them with extensibility in mind. Hey, thanks for the interest in this post, but just letting you know Creative Commons Attribution 4.0 International // Shape type definition using discriminated unions. This is useful when the value is not important. We would be introducing the same potential runtime error if we solved this Wether its bit-flags or stuff like `if(day < DaysOfWeek.Saturday)`. For example namespace (formerly "internal module") seems to be on its way out as there is no JavaScript equivalent (namespacing is often emulated with objects), and ECMAScript private fields could be taking over for private members. My personal choice to represent fixed values are TypeScript string enums that look something like this: The usage of string enums in my opinions avoids most of the pitfalls commonly attributed to TypeScript "default" enums. The enum itself is both a number and a defined constant. Enumerations (or enums) are a supported data type in TypeScript. As per Nicholas C. Zakas' "Bunny Theory of Code", once non-string enums are injected into the code-base, it is more likely they will be copied across files, leading to inconsistencies and the propagation of error-prone code. Lets create an enum in TypeScript to represent the days of the week: The enum is denoted using the enum keyword followed by the name of the enum (DayOfWeek) and then we define the constant values that we want to make available for the enum. Numeric Enums - Default. We are not comparing an Obiect with an enum, rather an "Object with as const". If you have read the previous section, you can compare and manipulate enum variant values, so you can write something like: In the if statement above, we are comparing an enum value with a string. Well, that's not entirely true. It turns out that even without the explicit predicate function, TypeScript can // Output: [Info]: This is an information message. Enums Can Introduce Tight Coupling: Enums create a strong coupling between the constant name and its associated value. This way your conditional statements using discriminated unions don't need to have hardcoded values and can have all the upsides of enums. This is something to consider, especially if files are shared between the frontend and backend of an application. } 4 digital products from validation to success and teach you how. This means that a function that takes user roles can accept any numeric value, which can cause security and performance problems. 2 Built on Forem the open source software that powers DEV and other inclusive communities. LogRocket is a frontend application monitoring solution that lets you replay problems as if they happened in your own browser. The server application types are defined separately from the auto-generated types to allow TS to perform typecheking in the GQL-resolvers. DEV Community A constructive and inclusive social network for software developers. Made with love and Ruby on Rails. First and foremost, here's what a union type looks like: Amazing! So far, weve only discussed enums that are numeric or explicitly assigning numbers to enum values, but an enum doesnt have to be a number value, it can be anything constant or computed value: Here weve made a string enum, and the generated code is a lot different: Now well no longer be able to pass in a number to the isItTheWeekend function, since the enum is not numeric, but we also cant pass in an arbitrary string, since the enum knows what string values are valid. Object.keys(Fruits) on it. Enums make the code more readable, maintainable, and self-explanatory. Why is type safety compromised in some cases? Writer, Speaker, FOSS Maintainer Author Strings may cause problems by variations in spelling and capitalisation. At first glance, enums are great - they allow you to store a set of read-only values in a concise, typesafe manner. So the object is the JavaScript (value space) part. element, we might model those values as a Fruits enum. Enums are used in most object-oriented programming languages like Java and C# and are now available in TypeScript too. Once unpublished, all posts by ivanzm123 will become hidden and only accessible to themselves. Get ready to be surprised! These can be use to "lock" the type/value of a string to only a certain values. NOT_FOUND: string; By default an enum is number based, starting at zero, and each option is assigned an increment by one. Each of these constant values is known as a member of the enum. The key difference between union types and enums (apart from their syntax), is that union types are purely compile time concepts, whereas enums emit JavaScript objects that will exist at runtime. 4 - Reverse Mapping from Value to Enum. Here's a code: enum IStatus { SUCCESS = 'success', FAILED = 'failed' } interface ResponseSuccess { databaseId: number sum: number from: number to: number } interface ResponseFail { errorMessage: string . Cookie Notice array: As opposed to enums, this has a few benefits: Enums can be challenging to use if you frequently need to check for existence of Yes, it's not a mistake. Metalhead Father of 2 Made with love and Ruby on Rails. Why? Here is what you can do to flag ivanzm123: ivanzm123 consistently posts content that violates DEV Community's Well, we met the problems with enums when we started using automatic type generation from GraphQL-schema. Now imagine a somewhat more abstract collection of options and you tell me which numeric value translates to what readable option in that enum. Co-Founder of This is Learning, Organizer of AarhusJS Once unpublished, this post will become invisible to the public and only accessible to Davide de Paolis. This way we can get enums without the runtime overhead, but there are a lot of pitfalls with const enum. For those who aren't yet familiar with TypeScript enums, here's a quick re-cap. And it will compile to nothing and in thee code it will have the hard code value, export const enum Enum { If ishanbagchi is not suspended, they can still re-publish their posts from their dashboard. All rights reserved. -1. 2023 Unflagging ivanzm123 will restore default visibility to their posts. This article will explore the potential problems with enums and suggest safer and more reliable alternatives. code would instead compile, but the constant fruit would be typed as Fruits. This is a valid TypeScript code, but it's not a good practice. */, /* So, if we are going to be setting value its better to set all of the values so that it is obvious what they are. This can become problematic if we were to do something like this: Weve made Thursday 2, so what does our generated JavaScript look like? Numeric enums I think it's worth mentioning that there is also the option to use const enum which will only leave the raw literals in the compiled code. Comparing enums with hardcoded values: While it is possible to compare enum values with hardcoded values, it is generally not recommended. But as 0. Therefore, we can pass in numbers to a function that expects an enum. When creating discriminated unions, you can use an enum as their kinds. Some code philosophers argue this goes against the ethos of enums, which are meant to be static lists and nothing more. // Produces -> [(0, 1, 2, Apple, Banana, Mango)]; // Helper type to get a type for possible keys of enum, // No type errors, and does not demand FruitEnumPojo.APPLE, // (["APPLE", "apple"], ["BANANA", "banana"], ["MANGO", "mango"]), // Type error thrown! fruit = Fruits[value as Fruits];. Before JavaScript gets their own enums, we are stuck with TypeScript. 2 - Constant vs Computed Values for Typescript Enums. type space: where TypeScript compile time types live, value space: where JavaScript runtime values live. But maybe I am missing something.. For example, I really can't figure out a scenario where I would need to write code myself to implement a ReverseMapping ( which is not done by Typescript automatically as for Numeric Enums) like described here. Syntax: Following is the syntax that we could use to initialize an enum in TypeScript- enum enum_name { // values.. } By understanding their benefits, limitations, and best practices, developers can leverage Enums effectively in their projects. Then Typescript would immediately notify the problem. ENUMs generate additional code at compile time, which increases the size of the final file. which in the end is not much different from having a bunch of static consts exported individually in a module. You have other better solutions as well, but this one should be a good one to replace the usage of an enum. This opens us up to a runtime error I guess that the amount of choices is not realy helping in this situation and might be one of the reasons why people are not embracing them. This allows us to perform a bitwise operation on them to create a new enum value in this case itll create 3, which is the value of the ReadWrite state. In the following TypeScript Playground example, the --strict flag (and Postada: I have been one of those people. Instead of using arbitrary values or strings to represent these options, you can use an enum to enforce type safety and provide a clear and predefined list of choices. Code must not use const enum; use plain enum instead. Specifying enum member values # TypeScript distinguishes three ways of specifying enum member values: Literal enum members are initialized: implicitly or; via number literals or string literals (explicitly). // because the types 'Role.User' and 'Role.Admin' have no overlap. Is it more readable in Typescript? 5 - Objects vs Typescript Enums. If you write export const enum you won't generate single value. You could also use enums in combination with interfaces, types of classes to encapsulate the behaviour of the enum, but, to be honest, I dont really see a usage of an enum. Using Enums in TypeScript is a great way to access particular parameters that are meant to be shared across multiple files, for example access levels of a particular user or a particular constant.. Then, when we reset the order at Wednesday, everything after that is incremented from the new starting position. Not a great gain. These values can't be reassigned later in the code. If we want to validate that the value is within the values listed in the Enum, we can simply iterate over the keys or values. While they may seem like a useful tool for defining a set of constant values, they are actually very dangerous. easier to access the enum values. As a result, its recommended that you dont use heterogeneous enums unless youre really sure its what you need. As you may have noticed, when the hasAccess(10) function is called, a numeric value is being passed that is not part of the enum Roles, this is allowed in TypeScript, and this is what is considered a problem, since it allows the entry of unexpected and unverified values which can cause security and performance problems in the app. An enum defines a set of named values, typically representing a collection of related constants or options. and the theme is licensed under TypeScript enums seem to fit right in with types, interfaces and all-around typesafety of TypeScript, but there are curiously underutilized in most ts codebases.
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