Enums should be objects with methods

[matthewadams]

Java's implementation of enums is quite good. The issue rwaldron/proposal-enum-definitions#5 describes it quite well for JavaScript. Let's please not forget to consider this. I, for one, would love to have JavaScript enums modeled after Java.

[rauschma]

I agree:

• I almost never use enums as lookup tables, but as collections of named values.
• Being able to define custom methods and properties is often helpful.
• I also like having unique values by default.

If you do want a lookup table, you can still get it via Java’s enum pattern:

class Mode {
  static user_r = new Mode(0b100000000);
  static user_w = new Mode(0b010000000);
  static user_x = new Mode(0b001000000);
  static group_r = new Mode(0b000100000);
  static group_w = new Mode(0b000010000);
  static group_x = new Mode(0b000001000);
  static all_r = new Mode(0b000000100);
  static all_w = new Mode(0b000000010);
  static all_x = new Mode(0b000000001);
  constructor(n) {
    this.n = n;
  }
}
assert.equal(
  Mode.user_r.n | Mode.user_w.n | Mode.user_x.n |
  Mode.group_r.n | Mode.group_x.n |
  Mode.all_r.n | Mode.all_x.n,
  0o755);
assert.equal(
  Mode.user_r.n | Mode.user_w.n | Mode.user_x.n |
  Mode.group_r.n,
  0o740);

As an enum, the class could look like this:

enum Mode {
  user_r(0b100000000);
  user_w(0b010000000);
  user_x(0b001000000);
  group_r(0b000100000);
  group_w(0b000010000);
  group_x(0b000001000);
  all_r(0b000000100);
  all_w(0b000000010);
  all_x(0b000000001);
  constructor(n) {
    this.n = n;
  }
}

The enum would also have many of the properties suggested by the proposal: Mode.keys, Mode.entries(), etc.

More examples and thoughts: https://2ality.com/2020/01/enum-pattern.html

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Alternatively, I also like the “algebraic data type” style: #6

I’d prefer not to mix it with “lookup table” style, though.