The folder structure of our enumeration app extends the structure of the validation app by adding the library files browserShims.js and Enumeration.mjs in the lib folder. Thus, we get the following folder structure with four files in the lib folder:

publicLibrary
  css
  lib
    browserShims.js
    errorTypes.mjs
    util.mjs
    Enumeration.mjs
  src
  index.html

In the browserShims.js file, we define a few extensions of the built-in JS object Array, representing a class, by adding two class-level functions (max and min), and two instance-level functions (clone and isEqualTo). These helper functions are used, e.g., in v/updateBook.mjs.

In the Enumeration.js file, discussed in the next section, we define a meta-class Enumeration for creating enumerations as instances of this meta-class with the help of statements like GenderEL = new Enumeration(["male", "female", "other"]).