In TypeScript, is it possible to add more stuff (properties, methods, etc.) to enum constants, like in Java?
Java example demonstrating adding of fields, methods and constructor:
public enum Planet {
MERCURY (3.303e+23, 2.4397e6),
VENUS (4.869e+24, 6.0518e6),
EARTH (5.976e+24, 6.37814e6),
MARS (6.421e+23, 3.3972e6),
JUPITER (1.9e+27, 7.1492e7),
SATURN (5.688e+26, 6.0268e7),
URANUS (8.686e+25, 2.5559e7),
NEPTUNE (1.024e+26, 2.4746e7);
private final double mass; // in kilograms
private final double radius; // in meters
Planet(double mass, double radius) {
this.mass = mass;
this.radius = radius;
}
private double mass() { return mass; }
private double radius() { return radius; }
// universal gravitational constant (m3 kg-1 s-2)
public static final double G = 6.67300E-11;
double surfaceGravity() {
return G * mass / (radius * radius);
}
double surfaceWeight(double otherMass) {
return otherMass * surfaceGravity();
}
// ...
}
Not using an enum, but you can get the same exact thing using a class and a few static members:
class Planet {
public static MERCURY = new Planet(3.303e+23, 2.4397e6);
public static VENUS = new Planet(4.869e+24, 6.0518e6);
public static EARTH = new Planet(5.976e+24, 6.37814e6);
public static MARS = new Planet(6.421e+23, 3.3972e6);
public static JUPITER = new Planet(1.9e+27, 7.1492e7);
public static SATURN = new Planet(5.688e+26, 6.0268e7);
public static URANUS = new Planet(8.686e+25, 2.5559e7);
public static NEPTUNE = new Planet(1.024e+26, 2.4746e7);
private mass: number;
private radius: number;
private constructor(mass: number, radius: number) {
this.mass = mass;
this.radius = radius;
}
public static G = 6.67300E-11;
public surfaceGravity(): number {
return Planet.G * this.mass / (this.radius * this.radius);
}
public surfaceWeight(otherMass: number) {
return otherMass * this.surfaceGravity();
}
}
console.log(Planet.MERCURY.surfaceGravity());
(code in playground)
In java for each item in the enum a static instance is created, which means that this indeed does the same thing, it's just that java has a nicer syntax for defining enums.
Here's a version with the equivalent Planet.values()
which java will generate:
class Planet {
public static MERCURY = new Planet(3.303e+23, 2.4397e6);
public static VENUS = new Planet(4.869e+24, 6.0518e6);
...
private static VALUES: Planet[] = [];
private mass: number;
private radius: number;
private constructor(mass: number, radius: number) {
this.mass = mass;
this.radius = radius;
Planet.VALUES.push(this);
}
public static values() {
return Planet.VALUES;
}
...
}
Here's a way to implement the valueOf
:
public static valueOf(name: string): Planet | null {
const names = Object.keys(this);
for (let i = 0; i < names.length; i++) {
if (this[names[i]] instanceof Planet && name.toLowerCase() === names[i].toLowerCase()) {
return this[names[i]];
}
}
return null;
}
Unfortunately it's not possible. You can just assign property names
See this reference for the TypeScript spec https://github.com/microsoft/TypeScript/blob/30cb20434a6b117e007a4959b2a7c16489f86069/doc/spec-ARCHIVED.md#a7-enums
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