JavaScript Mapping for Enumerations

JavaScript does not have an enumerated type, so a Slice enumeration is emulated using JavaScript objects where each enumerator is an instance of the same type. For example:

enum Fruit { Apple, Pear, Orange }

The generated code is equivalent to the following:

class Fruit { ... }
Fruit.Apple = new Fruit("Apple", 0);
Fruit.Pear = new Fruit("Pear", 1);
Fruit.Orange = new Fruit("Orange", 2);

class Fruit
{
    static readonly Apple:Fruit;
    static readonly Pear:Fruit;
    static readonly Orange:Fruit;
        
    static valueOf(value:number):Fruit;
    equals(other:any):boolean;
    hashCode():number;
    toString():string;
        
    readonly name:string;
    readonly value:number;
}

Each enumerator defines name and value properties that supply the enumerator's name and ordinal value, respectively. Enumerators also define hashCode, equals and toString methods, and the enumerated type itself defines a valueOf method that converts ordinal values into their corresponding enumerators.

Suppose we modify the Slice definition to include a custom enumerator value:

enum Fruit { Apple, Pear = 3, Orange }

The generated code changes accordingly:

class Fruit = { ... };
Fruit.Apple = new Fruit("Apple", 0);
Fruit.Pear = new Fruit("Pear", 3);
Fruit.Orange = new Fruit("Orange", 4);

Given the above definitions, we can use enumerated values as follows:

const f1 = Fruit.Apple;
const f2 = Fruit.Orange;

if(f1 === Fruit.Apple)   // Compare with constant
{
    // ...
}

if(f1 === f2)            // Compare two enums
{
    // ...
}

switch(f2)               // Switch on enum
{
    case Fruit.Apple:
        // ...
        break;
    case Fruit.Pear:
        // ...
        break;
    case Fruit.Orange:
        // ...
        break;
}
 
const f = Fruit.valueOf(3); // Convert an ordinal value to its enumerator, or undefined if no match
console.log(f.name + " = " + f.value); // Outputs "Pear = 3"

Note that the generated type may contain other members, which we have not shown. These members are internal to the Ice run time and you must not use them in your application code (because they may change from release to release).

See Also

• Enumerations
• JavaScript Mapping for Structures
• JavaScript Mapping for Sequences
• JavaScript Mapping for Dictionaries