Allow only specific string values with TypeScript type
The main advantage of using enums over string literal types is that they make your code easier to read and organize The whole purpose of enums is to define a group of named and related constants I ve also written an article on how to check if a string is in a union Additional Resources You can learn more about the related topics by checking out the following tutorials
How to allow only certain string values for variables or constants in , As you can see from the above code that now we can have any string values assigned to the role variable This is fine for now But what if we need to restrict the values of the role variable to only hold certain string values like owner admin or user To achieve this functionality in TypeScript we can use string literal union types in
TypeScript TSConfig Option moduleResolution
Specify the module resolution strategy node16 or nodenext for modern versions of Node js Node js v12 and later supports both ECMAScript imports and CommonJS require which resolve using different algorithms These moduleResolution values when combined with the corresponding module values picks the right algorithm for each resolution based on whether Node js will see an import or require
TypeScript Handbook Literal Types, A literal is a more concrete sub type of a collective type What this means is that Hello World is a string but a string is not Hello World inside the type system There are three sets of literal types available in TypeScript today strings numbers and booleans by using literal types you can allow an exact value which a string number or boolean must have
How to dynamically assign properties to an object in TypeScript
How to dynamically assign properties to an object in TypeScript, Table of contents The problem with dynamically assigning properties to objects Solution 1 Explicitly type the object at declaration time Solution 2 Use an object index signature Solution 3 Use the Record Utility Type Solution 4 Use the Map data type Solution 5 Consider an optional object property
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TypeScript Documentation Variable Declaration
TypeScript Documentation Variable Declaration Var declarations Declaring a variable in JavaScript has always traditionally been done with the var keyword var a 10 As you might ve figured out we just declared a variable named a with the value 10 We can also declare a variable inside of a function function f
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String literals are one of the most straightforward and powerful tools of TypeScript But until v3 4 it was impossible to list its accepted values Developers needed to fall back to enums Not a problem anymore On an imaginary page there is a certain set of user types namely Admin Editor Reader and Anonymous How to list the possible values of a string literal union type in . We then declare an array called myArray of type AllowedValues which means it can only contain elements that are of type AllowedValues If we try to add an element to the array that is not part of the allowed set Typescript will throw a compile time error myArray push value4 Compile time error Argument of type A literal enum member is a constant enum member with no initialized value or with values that are initialized to any string literal e g foo bar baz any numeric literal e g 1 100 a unary minus applied to any numeric literal e g 1 100 When all members in an enum have literal enum values some special semantics come into play
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