How to implement Swift-like enums with associated values in JavaScript?

Question

The Swift language has a fantastic enum support. Not only can one define a standard enum with cases, but cases can have optional values "associated to them."

For example, taken from the Swift docs:

enum Barcode {     case UPCA(Int, Int, Int, Int)     case QRCode(String)     case Other } 

Such that one could create a Barcode enum by passing in a value, like so:

var productBarcode = Barcode.UPCA(8, 85909, 51226, 3)

and also switch on productBarcode at a later date to retrieve the associated value (a tuple of ints).

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I have been trying to implement this kind of enum system in JavaScript (ES5, in particular), but am hitting a wall. What is the best way to structure an enum system, especially one with associated values?

Answer 1

You can use a discriminated union for this. This example uses Typescript, but the concept would be similar for Javascript just without the type safety.

interface UPCA {     kind: "UPCA";     numberSystem: number;     manufacturer: number;     item: number;     checkDigit: number; }  interface QRCode {     kind: "QRCode";     data: string; }  interface Other {     kind: "Other"; }  type Barcode = UPCA | QRCode | Other; 

You can then switch over a value of Barcode and access the associated values after checking the discriminate.

function printBarcode(barcode: Barcode) {   switch (barcode.kind) {     case "UPCA":       console.log(`UPCA: ${barcode.numberSystem}-${barcode.manufacturer}`);       break;     case "QRCode":       console.log(`QRCode: ${barcode.data}`);       break;     case "Other":       console.log("Other barcode");       break;   }  }