Object.keys allows you to enumerate the properties of an object, returning you an array of string which represent the property names. Especially const enums, they don't have an object at all. TypeScript 2.4 implemented one of the most requested features: string enums, or, to be more precise, enums with string-valued members. Yes, keyof typeof is correct. A TypeScript string enum for compile-time safety when working with event.key - nfriend/ts-key-enum ... ts-key-enum. TypeScript Data Type - Enum. Object.keys. If you’ll log above enum, it’ll show the following output: { 1: "Up" 3: "Left" Down: "DownValue" Left: 3 Right: "RightValue" Up: 1 } Here you can see that for the numeric member, typescript created object with reverse mapping as well. a collection of related values that can be numeric or string values. In simple words, enums allow us to declare a set of named constants i.e. Using `enum` values as strictly typed object keys 25 Feb 2020, typescript, enum, mapped types, improve this page In TypeScript, it’s often useful to define interfaces or complex (structured) types whose properties (or keys) may only be values of a previously defined enum type. It is now possible to assign a string value to an enum member: enum MediaTypes {JSON = "application/json", XML = "application/xml"} It represents the type of the property K of the type T. Therefore using keyof myEnum results in generic string keys. The last step is very important: TypeScript has limited reflection ability, so this is a case where we have to explicitly provide the enum type for object type fields, input type fields, args, and the return type of queries and mutations: @ InputType class JourneyInput {@ Field (type => Direction) // it's very important direction: Direction;} ... (Sunday being 0, Saturday being 6), but the object also has number keys with a string value representing the named constant. Most object-oriented languages like Java and C# use enums. Enums or enumerations are a new data type supported in TypeScript. We’ll first see how typescript create an object for Heterogeneous enum. ... typescript best practices - redefine type vs use existing types' parameters. The end result is a JavaScript object that contains every enum value. Typescript requires that enums have number value types (hopefully soon, this will also include string value types). This is now available in TypeScript too. String Enums in TypeScript October 27, 2017. A TypeScript string enum for compile-time safety when working with event.key. Instead, we'll require that the key actually exists on the type of the object that is passed in: function prop < T, K extends keyof T >(obj: T, key: K) {return obj[key];} TypeScript now infers the prop function to have a return type of T[K], a so-called indexed access type or lookup type. Conditionally show content using an Enum and *ngIf; Get all the values of an enum as an Array Intro You can skip the next block of text if you just want to get the actual details (I respect that) I love using Enums in TypeScript as I am a terrible developer with a terrible memory and let my editor's auto complete do 80% of my job. A few tips on how to use enums in TypeScript, and some gotcha's to watch out for. Sometimes it is still useful to just loop through each property on an object in order to do something. I find that I use it for unit testing, but there’s other applications, too. myEnum can be used as a type but it references the values of the enum. 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