So, for example, we could have a type defined like so: We can then make use of the type as, say, a function parameter, and the language can check that these exact types are passed at compile time to the function when instantiated. We should also note that, to emit the mapping code regardless of const enums, we can turn on the preserveConstEnums compiler option in our tsconfig.json file. They also allow for a meaningful and readable value at runtime, independent of the name of the enum member. can you confirm that the solution proposed by Ester works for string enums too? For completely string-based enums, we cannot omit any initializers, as all enum members must come with values. This means that subsequent values are incremented by adding one to the preceding numeric constants, in that order. All Rights Reserved. Check if a Value exists in an Enum in TypeScript, // ['0', '1', '2', 'Small', 'Medium', 'Large'], // ['Small', 'Medium', 'Large', 0, 1, 2], '2 is contained in the values of the enum'. React alert notification example| primereact toast tutorials, Primeng toast example | Angular Popup component, Primeng Progressbar tutorial| p-progress bar example, Frequently Used Array Examples - Javascript|Typescript, Generates Javascript Documentation - ESDoc Tool, The best way to convert Array to JSON in typescript with example, Javascript Es6 Set tutorials | Typescript Set Examples, ES6 Map Class Tutorials in Javascript Examples Typescript. mv fails with "No space left on device" when the destination has 31 GB of space remaining. Like this article? Your solution. Heterogeneous enum: Heterogeneous enums are enums that contain both string and numeric values. Is there a way to generate energy using a planet's angular momentum. Most object-oriented languages like Java and C# use enums. Watch the recording for a deep dive on some new features of TypeScript 4.4. This does not work with string enums because they are not reverse mapped: It seems like this approach works with string enums in 2021. Const enum members are also inlined at use sites. You can check my other posts on typescript Enum objectif(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[728,90],'cloudhadoop_com-medrectangle-3','ezslot_6',117,'0','0'])};if(typeof __ez_fad_position != 'undefined'){__ez_fad_position('div-gpt-ad-cloudhadoop_com-medrectangle-3-0')}; There are many ways we can check string exists in enumeration. To check if a TypeScript array contains an object: Pass a function to the Array.find () method. Since I've moved from programming to fulltime UX Design I can't verify this anymore. Let us see an example below: Const-based enums can only use constant enum expressions and are not added during compilation, which is unlike regular enum declarations. 
For number-based enums, members are distinct from each other due to their auto-incrementing nature. Can a human colony be self-sustaining without sunlight using mushrooms? Share it on Social Media. String enums are flexible in that we can either add key-values as enums, or just keys, if the key-values are the same and if we do not care about the case sensitivity of our enums. Throughout this article, we will focus on string-based enums. See an example below. So my enum in my original answer becomes: For clarity, I like to break the values and includes calls onto separate lines. Array.find will return the object if the conditional check is satisfied at least once. Ways to skip test case execution in Gradle project build. For instance, whenever we make use of an enum member in our code for validation purposes, TypeScript checks statically that no other values are used. I receive a number type = 3 and have to check if it exists in this enum: The best way I found is by getting all Enum Values as an array and using indexOf on it. We can also picture enums as artificially created types that contain a finite set of values, just like we have the boolean type, which contains only false and true values. if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[300,250],'cloudhadoop_com-medrectangle-4','ezslot_7',137,'0','0'])};if(typeof __ez_fad_position != 'undefined'){__ez_fad_position('div-gpt-ad-cloudhadoop_com-medrectangle-4-0')};ES7, latest javascript language introduced includes method. Error trying to diff '[object Object]'. Software engineer. Copyright var creditsyear = new Date();document.write(creditsyear.getFullYear()); The main interesting part is the EnumClass[keyof EnumClass] return type. The TypeScript documentation contains more details on constant versus computed enums, if youre interested. So fa Issue I want to convert current data into 'yyyy-MM-dd' format in .ts file Issue I am having this header which on scroll, I want to change the background to a differ Issue I want to make 2 API calls in Parallel and then the third immediately after that. In summary, for constant enums, the enum member value can be the first member without an initializer or must have an initializer which is numeric, if it has other enum members preceding it. We can use this construct as shown in the example below: Doing this, we get an object that is read-only and protected. This works because when you compile the above enum, it generates the below object: According to sandersn the best way to do this would be: There is a very simple and easy solution to your question: Type assertion is un-avoidable. When using string enums in TypeScript, we do not necessarily need to know the exact strings each enum value contains. type direction = keyof typeof Direction; The comment should be: Let us explore an example below where we can check if an operation succeeded or failed via a boolean check and with the use of an enum type declaration: To create a type whose values are the keys of enum members, we can make use of keyof with the typeof method. See an illustration below: With const-based enums, we can avoid the generated code by the TS compiler, which is useful when accessing enum values. Perfect answer. Please refer to the TypeScript documentation for more information on number-based enums. How do I call 2 API in parallel and the third right after that in RXJS. Yes this is a bad example and should not be used as is. @mamacdon, absolutely. 2021 FaqCode4U.com. The numeric enum in the example has no initial values, so the first value is // this is same as If key!=value, it would check by key. currently it is defined as such: ok, thanks for the explanation. What drives the appeal and nostalgia of Margaret Thatcher within UK Conservative Party? For the case of computed enums, they can be initialized via expressions. This is where legacy support comes into the picture. But this is not the case for numeric enums, which end up as only plain numbers and therefore might not too useful. Somehow I allways get the following Issue Code is: const foo = (foo: string) => { const result = [] result.push(foo) Issue with *ngFor, I cannot fetch the data from my component.ts to my component.html The Issue I installed CDK Virtual Scroller in my ionic 5.3.3 project: npm add @angular/cdk T Issue Recently I changed my custom input components to use react useFormContext instead o Issue I have a function that when calling it opens a modal from ngbModal, I have imported Issue I am trying to create a basic web component in Angular with Angular Elements. Due to the auto-incrementing behavior of number-based enums, there exist a caveat for these enums when there are no initializers. Usually, enum types come in handy when we intend to declare certain types that must satisfy certain criteria defined in the enum declarations. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. What is "not assignable to parameter of type never" error in TypeScript? After compilation, they are represented as shown below: As we can see from the above, the enum member values are inlined by TS. the unnecessary values. They can also have more than one member value, whereby the first member must be a numeric constant. numeric enums - the returned array contains the keys and the values. Trending is based off of the highest score sort and falls back to it if no posts are trending. We will update the comment as soon as possible. Actually this case works only because of a coincident. Values are initialized implicitly via number literals, or explicitly via string literals, Constant enum members: Const-based enum members can only be accessed using a string literal. This is applicable when certain enum members only have their corresponding values. corresponding value. angularfix. This is probably the best and safest answer. Use tab to navigate through the menu items. If you click a merchant link and buy a product or service on their website, we This means that they are automatically assigned the value of 0. When adding a new disk to RAID 1, why does it sync unused space? Numeric enum: Numeric enums are number-based enums i.e. The auto-initialized value on an enum is its property name. For an example of how to use this construction, suppose we have the following enum: Direction is both a type as well as a runtime object. There can be a tension between type safety and readable code. For constant enums, the enum must be the first member and it has no initializer. Laymen's description of "modals" to clients. Enums are not a new concept in programming. How to help my players track gold in multiple currencies? To get the number value of an enum member from a string value, you can use this: We can use these values to make simple string comparisons, e.g. The wonderful thing about working with a typed language like TypeScript and using a feature like this is that popular IDEs like Visual Studio Code can help us choose enum values from a list of values via autocomplete. Instead, in string-based enums, we can assign string values directly to enum members. @TimSchoch Yes! In typescript, Enum object holds the following format as below, Numbers can be checked in enum in many ways, using in operator For const enums or enums of other types, see this answer above. they store string values as numbers. enums are not natively supported in JavaScript, but there is a workaround that lets us replicate their behavior in the language using the Object.freeze construct, since TypeScript treats enums as if they were real objects (although applicable for non-const enums at runtime). How do I check whether a checkbox is checked in jQuery? Instead, the values of its members are used directly. See @Xiv's answer below: I like to use two lines: const options: string[] = Object.values(TheEnum); const isInTheEnum = options.includes(theValue); I think this one is the most readable. methods. I receive a number type = 3 and have to check if it exists in this enum: The best way I found is by getting all Enum Values as an array and using indexOf on it. This is especially useful when we are tasked with making comparisons between or among values from an enum, or even in their regular usage. Enum is a new datatype introduced in Javascript/typescript which holds strings or numbers only. String enums are heavily used in JSON objects for validating API calls to do things like ensure parameters are passed correctly. The methods return an array containing the object's keys and values, on which we can use the includes method to check if a specific value is contained in the enum's values. We can generate a type predicate for Direction and use it like so: If you there to find how to check union contain specific value, there is solution: To subscribe to this RSS feed, copy and paste this URL into your RSS reader. As a result of their usefulness and advantages in other languages, enums were introduced and added to the TypeScript landscape. You can either use this tsconfig.json config: Note: Only a member of this blog may post a comment. Connect and share knowledge within a single location that is structured and easy to search. But if the keys differ from the values it doesn't work. We are able to do this because TypeScript provides Enums are not a new concept in programming, to optimize your application's performance, need to be fully evaluated at compile time, TypeScript version 2.4 supports string-based enums, produce a union type out of the literal types of its values, example of how enums behave as objects at runtime, reverse mapping for number-valued members, it is not clear why you would ever want to do this, more details on constant versus computed enums, Developing a 2D mobile game as a mobile app developer, Using React Native ScrollView to create a sticky header, Fleet: A build tool for improving Rusts Cargo, Literal enum members: Literal enum types are enum types where each member either has no initializer, or an initializer that specifies a numeric literal, a string literal, or an identifier naming another member in the enum type. How can I determine if a string is part of an enum? String enum: String enums are similar to numeric enums, except that the enum values are initialized with string values rather than numeric values. Instead, typecasting the Object.values() output to an array of strings is in-fact very much real. However, enums are quite unique and specific to TS, in that they are not a typed extension of, equivalent to, or correspond with a specific feature in the JavaScript language, despite TS being a typed superset of JS. A subtle difference between number-based enums and string-based enums is that for number-based enums, there is reverse mapping for number-valued members. It works for strings too. If we leave off the initializers, we have this below: As we can see from the above examples, accessing the members of an enum is as simple as accessing the properties of objects. and If you are using TypeScript, you can use an actual enum. String-based enums were only introduced to TypeScript in version 2.4, and they made it possible to assign string values to an enum member. The, Thank you Ester for your answer. As we may already know, most programming languages like Java, C, and so on, have the concept of enums defined in their core. In simple words, enums allow us to declare a set of named constants i.e. String enums are serializable over transfer protocols and are easily debuggable since they are just strings, after all. Enums offer a more self-descriptive option than making use of boolean values. The only difference is in their behavior and usage. : As we mentioned earlier, logging members of numeric enums is not so useful because we are seeing only numbers. If we were to debug a program, it is easier to read string values rather than numeric values. rev2022.7.21.42639. Enum members can also become types as well. This, therefore, infers that const enums cannot have computed members. Sometimes, It is necessary to check whether a declared string or number exists in an Enum object. What's the use of the 100 k resistors in this schematic? Unfortunately, this does not apply for string-based enums. Note that this does NOT work for string enums if the enum uses string initializers with different values than the enum member names. For anyone who comes here looking to validate if a string is one of the values of an enum and type convert it, I wrote this function that returns the proper type and returns undefined if the string is not in the enum. Reverse mapping allows us to check if a given value is valid in the context of the enum. Thanks again. If you want this to work with string enums, you need to use Object.values(ENUM).includes(ENUM.value) because string enums are not reverse mapped, according to https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-4.html: If you get an error for: Property 'values' does not exist on type 'ObjectConstructor', then you are not targeting ES2017. numeric enum. One question: what's the purpose of the. Check whether the identifier of the object is equal to a specific value and return true if it is. To do this in TypeScript, we can make use of the as const method with a regular object. I've found that whenever I need to check if a value exists in an enum, I don't really need an enum and that a type is a better solution. We mentioned earlier that the reason for this is that non-const enums have object-like behavior. @crowd, let me know if I the accepted answer is still the way to go in 2019! Enums or enumerations are a new data type supported in TypeScript. Enums in TypeScript are real objects and exist at runtime. The display of third-party trademarks and trade names on this site does not Therefore, this limits our ability to use number-based enums in JSON objects, since it is usually not possible to compute the names of these kinds of enum members. Let us see the transpiled output below: String enums can be easily inferred from their indices or by looking at the initializer of their first member. Unfortunately, you can only use this approach to get tha names of numeric enums. Enum member values can either be constant or computed, as we have earlier discussed. Object.keys This is now available in TypeScript too. This sort of mirrors the idea behind enums, since they are meant to have a definite number of fixed values for a given variable declaration. TypeScript brings type safety to JavaScript. How to check does the given string exists as a value in a string enum in Typescript? As we mentioned earlier, while enums are numerically based by default, TypeScript version 2.4 supports string-based enums. Then you can check it using in. It is also important to point out that while enums can be mixed with string and numeric members (heterogeneous), it is not clear why you would ever want to do this. On their own, they are usually not so useful, but when they are combined with union types, they become immensely powerful. On line 13, StatusCodes["OK"] = 200 is also equal to StatusCodes[200] = "OK". This solution looks clear at first glance but it is definitely bug-prone. There is also the issue of loose typing when using these enums types, as the values that are allowed statically are not only those of the enum members any number is accepted. 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They either need to be declared first or must succeed numeric enums initialized with number-based constants, also applicable in heterogenous enums. In modern TypeScript, there is an approach of implementing string-based enums so that they are backwards compatible in the JavaScript landscape. If you are in need of a general introduction to enum types or an overview of ways enums could be misused in the language, the LogRocket blog has you covered. You could also use a Set or possibly even enumClass itself by checking if the input exists in the enumClass. To understand this better, let us look at the compiled output of a number-based enum: If we look at lines 13-17 above, we will see that we can resolve a value by its key, and a key by its value. When such a type is an enum in TypeScript, it returns the original type of the enum where EnumClass is the type of the runtime enum class. At runtime, string-based enums behave just like objects and can easily be passed to functions like regular objects. Cheers. An enum is an object, In operator returns true if a property exists in an object, else return false, Enum index syntax - return strings if the number exists, else undefined returned, if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[250,250],'cloudhadoop_com-banner-1','ezslot_8',126,'0','0'])};if(typeof __ez_fad_position != 'undefined'){__ez_fad_position('div-gpt-ad-cloudhadoop_com-banner-1-0')};and console output is. includes() method simply checks and returns true -if exists, false- not exists. Enums in TypeScript are real objects and exist at runtime. It avoids the use of, aha! Join 6,000 subscribers and get a daily digest of full stack tutorials delivered to your inbox directly.No spam ever. How to get an enum value from a string value in Java. If you are new to the JavaScript/TypeScript landscape, you might be wondering what Enums are. I found one alternative that wasn't mentioned so thought I'd share my fix for it: I find this more truthful because we usually come in typesafe(with a string) and want to compare it to the enum; it'd be a bit reckless to typecast it to any(reason: never do this) or Vehicle(reason: likely untruthful).
For number-based enums, members are distinct from each other due to their auto-incrementing nature. Can a human colony be self-sustaining without sunlight using mushrooms? Share it on Social Media. String enums are flexible in that we can either add key-values as enums, or just keys, if the key-values are the same and if we do not care about the case sensitivity of our enums. Throughout this article, we will focus on string-based enums. See an example below. So my enum in my original answer becomes: For clarity, I like to break the values and includes calls onto separate lines. Array.find will return the object if the conditional check is satisfied at least once. Ways to skip test case execution in Gradle project build. For instance, whenever we make use of an enum member in our code for validation purposes, TypeScript checks statically that no other values are used. I receive a number type = 3 and have to check if it exists in this enum: The best way I found is by getting all Enum Values as an array and using indexOf on it. We can also picture enums as artificially created types that contain a finite set of values, just like we have the boolean type, which contains only false and true values. if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[300,250],'cloudhadoop_com-medrectangle-4','ezslot_7',137,'0','0'])};if(typeof __ez_fad_position != 'undefined'){__ez_fad_position('div-gpt-ad-cloudhadoop_com-medrectangle-4-0')};ES7, latest javascript language introduced includes method. Error trying to diff '[object Object]'. Software engineer. Copyright var creditsyear = new Date();document.write(creditsyear.getFullYear()); The main interesting part is the EnumClass[keyof EnumClass] return type. The TypeScript documentation contains more details on constant versus computed enums, if youre interested. So fa Issue I want to convert current data into 'yyyy-MM-dd' format in .ts file Issue I am having this header which on scroll, I want to change the background to a differ Issue I want to make 2 API calls in Parallel and then the third immediately after that. In summary, for constant enums, the enum member value can be the first member without an initializer or must have an initializer which is numeric, if it has other enum members preceding it. We can use this construct as shown in the example below: Doing this, we get an object that is read-only and protected. This works because when you compile the above enum, it generates the below object: According to sandersn the best way to do this would be: There is a very simple and easy solution to your question: Type assertion is un-avoidable. When using string enums in TypeScript, we do not necessarily need to know the exact strings each enum value contains. type direction = keyof typeof Direction; The comment should be: Let us explore an example below where we can check if an operation succeeded or failed via a boolean check and with the use of an enum type declaration: To create a type whose values are the keys of enum members, we can make use of keyof with the typeof method. See an illustration below: With const-based enums, we can avoid the generated code by the TS compiler, which is useful when accessing enum values. Perfect answer. Please refer to the TypeScript documentation for more information on number-based enums. How do I call 2 API in parallel and the third right after that in RXJS. Yes this is a bad example and should not be used as is. @mamacdon, absolutely. 2021 FaqCode4U.com. The numeric enum in the example has no initial values, so the first value is // this is same as If key!=value, it would check by key. currently it is defined as such: ok, thanks for the explanation. What drives the appeal and nostalgia of Margaret Thatcher within UK Conservative Party? For the case of computed enums, they can be initialized via expressions. This is where legacy support comes into the picture. But this is not the case for numeric enums, which end up as only plain numbers and therefore might not too useful. Somehow I allways get the following Issue Code is: const foo = (foo: string) => { const result = [] result.push(foo) Issue with *ngFor, I cannot fetch the data from my component.ts to my component.html The Issue I installed CDK Virtual Scroller in my ionic 5.3.3 project: npm add @angular/cdk T Issue Recently I changed my custom input components to use react useFormContext instead o Issue I have a function that when calling it opens a modal from ngbModal, I have imported Issue I am trying to create a basic web component in Angular with Angular Elements. Due to the auto-incrementing behavior of number-based enums, there exist a caveat for these enums when there are no initializers. Usually, enum types come in handy when we intend to declare certain types that must satisfy certain criteria defined in the enum declarations. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. What is "not assignable to parameter of type never" error in TypeScript? After compilation, they are represented as shown below: As we can see from the above, the enum member values are inlined by TS. the unnecessary values. They can also have more than one member value, whereby the first member must be a numeric constant. numeric enums - the returned array contains the keys and the values. Trending is based off of the highest score sort and falls back to it if no posts are trending. We will update the comment as soon as possible. Actually this case works only because of a coincident. Values are initialized implicitly via number literals, or explicitly via string literals, Constant enum members: Const-based enum members can only be accessed using a string literal. This is applicable when certain enum members only have their corresponding values. corresponding value. angularfix. This is probably the best and safest answer. Use tab to navigate through the menu items. If you click a merchant link and buy a product or service on their website, we This means that they are automatically assigned the value of 0. When adding a new disk to RAID 1, why does it sync unused space? Numeric enum: Numeric enums are number-based enums i.e. The auto-initialized value on an enum is its property name. For an example of how to use this construction, suppose we have the following enum: Direction is both a type as well as a runtime object. There can be a tension between type safety and readable code. For constant enums, the enum must be the first member and it has no initializer. Laymen's description of "modals" to clients. Enums are not a new concept in programming. How to help my players track gold in multiple currencies? To get the number value of an enum member from a string value, you can use this: We can use these values to make simple string comparisons, e.g. The wonderful thing about working with a typed language like TypeScript and using a feature like this is that popular IDEs like Visual Studio Code can help us choose enum values from a list of values via autocomplete. Instead, in string-based enums, we can assign string values directly to enum members. @TimSchoch Yes! In typescript, Enum object holds the following format as below, Numbers can be checked in enum in many ways, using in operator For const enums or enums of other types, see this answer above. they store string values as numbers. enums are not natively supported in JavaScript, but there is a workaround that lets us replicate their behavior in the language using the Object.freeze construct, since TypeScript treats enums as if they were real objects (although applicable for non-const enums at runtime). How do I check whether a checkbox is checked in jQuery? Instead, the values of its members are used directly. See @Xiv's answer below: I like to use two lines: const options: string[] = Object.values(TheEnum); const isInTheEnum = options.includes(theValue); I think this one is the most readable. methods. I receive a number type = 3 and have to check if it exists in this enum: The best way I found is by getting all Enum Values as an array and using indexOf on it. This is especially useful when we are tasked with making comparisons between or among values from an enum, or even in their regular usage. Enum is a new datatype introduced in Javascript/typescript which holds strings or numbers only. String enums are heavily used in JSON objects for validating API calls to do things like ensure parameters are passed correctly. The methods return an array containing the object's keys and values, on which we can use the includes method to check if a specific value is contained in the enum's values. We can generate a type predicate for Direction and use it like so: If you there to find how to check union contain specific value, there is solution: To subscribe to this RSS feed, copy and paste this URL into your RSS reader. As a result of their usefulness and advantages in other languages, enums were introduced and added to the TypeScript landscape. You can either use this tsconfig.json config: Note: Only a member of this blog may post a comment. Connect and share knowledge within a single location that is structured and easy to search. But if the keys differ from the values it doesn't work. We are able to do this because TypeScript provides Enums are not a new concept in programming, to optimize your application's performance, need to be fully evaluated at compile time, TypeScript version 2.4 supports string-based enums, produce a union type out of the literal types of its values, example of how enums behave as objects at runtime, reverse mapping for number-valued members, it is not clear why you would ever want to do this, more details on constant versus computed enums, Developing a 2D mobile game as a mobile app developer, Using React Native ScrollView to create a sticky header, Fleet: A build tool for improving Rusts Cargo, Literal enum members: Literal enum types are enum types where each member either has no initializer, or an initializer that specifies a numeric literal, a string literal, or an identifier naming another member in the enum type. How can I determine if a string is part of an enum? String enum: String enums are similar to numeric enums, except that the enum values are initialized with string values rather than numeric values. Instead, typecasting the Object.values() output to an array of strings is in-fact very much real. However, enums are quite unique and specific to TS, in that they are not a typed extension of, equivalent to, or correspond with a specific feature in the JavaScript language, despite TS being a typed superset of JS. A subtle difference between number-based enums and string-based enums is that for number-based enums, there is reverse mapping for number-valued members. It works for strings too. If we leave off the initializers, we have this below: As we can see from the above examples, accessing the members of an enum is as simple as accessing the properties of objects. and If you are using TypeScript, you can use an actual enum. String-based enums were only introduced to TypeScript in version 2.4, and they made it possible to assign string values to an enum member. The, Thank you Ester for your answer. As we may already know, most programming languages like Java, C, and so on, have the concept of enums defined in their core. In simple words, enums allow us to declare a set of named constants i.e. String enums are serializable over transfer protocols and are easily debuggable since they are just strings, after all. Enums offer a more self-descriptive option than making use of boolean values. The only difference is in their behavior and usage. : As we mentioned earlier, logging members of numeric enums is not so useful because we are seeing only numbers. If we were to debug a program, it is easier to read string values rather than numeric values. rev2022.7.21.42639. Enum members can also become types as well. This, therefore, infers that const enums cannot have computed members. Sometimes, It is necessary to check whether a declared string or number exists in an Enum object. What's the use of the 100 k resistors in this schematic? Unfortunately, this does not apply for string-based enums. Note that this does NOT work for string enums if the enum uses string initializers with different values than the enum member names. For anyone who comes here looking to validate if a string is one of the values of an enum and type convert it, I wrote this function that returns the proper type and returns undefined if the string is not in the enum. Reverse mapping allows us to check if a given value is valid in the context of the enum. Thanks again. If you want this to work with string enums, you need to use Object.values(ENUM).includes(ENUM.value) because string enums are not reverse mapped, according to https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-4.html: If you get an error for: Property 'values' does not exist on type 'ObjectConstructor', then you are not targeting ES2017. numeric enum. One question: what's the purpose of the. Check whether the identifier of the object is equal to a specific value and return true if it is. To do this in TypeScript, we can make use of the as const method with a regular object. I've found that whenever I need to check if a value exists in an enum, I don't really need an enum and that a type is a better solution. We mentioned earlier that the reason for this is that non-const enums have object-like behavior. @crowd, let me know if I the accepted answer is still the way to go in 2019! Enums or enumerations are a new data type supported in TypeScript. Enums in TypeScript are real objects and exist at runtime. The display of third-party trademarks and trade names on this site does not Therefore, this limits our ability to use number-based enums in JSON objects, since it is usually not possible to compute the names of these kinds of enum members. Let us see the transpiled output below: String enums can be easily inferred from their indices or by looking at the initializer of their first member. Unfortunately, you can only use this approach to get tha names of numeric enums. Enum member values can either be constant or computed, as we have earlier discussed. Object.keys This is now available in TypeScript too. This sort of mirrors the idea behind enums, since they are meant to have a definite number of fixed values for a given variable declaration. TypeScript brings type safety to JavaScript. How to check does the given string exists as a value in a string enum in Typescript? As we mentioned earlier, while enums are numerically based by default, TypeScript version 2.4 supports string-based enums. Then you can check it using in. It is also important to point out that while enums can be mixed with string and numeric members (heterogeneous), it is not clear why you would ever want to do this. On their own, they are usually not so useful, but when they are combined with union types, they become immensely powerful. On line 13, StatusCodes["OK"] = 200 is also equal to StatusCodes[200] = "OK". This solution looks clear at first glance but it is definitely bug-prone. There is also the issue of loose typing when using these enums types, as the values that are allowed statically are not only those of the enum members any number is accepted. 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They either need to be declared first or must succeed numeric enums initialized with number-based constants, also applicable in heterogenous enums. In modern TypeScript, there is an approach of implementing string-based enums so that they are backwards compatible in the JavaScript landscape. If you are in need of a general introduction to enum types or an overview of ways enums could be misused in the language, the LogRocket blog has you covered. You could also use a Set