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:

Slice

enum Fruit { Apple, Pear, Orange };

The generated JavaScript code is equivalent to the following:

JavaScript

var Fruit = function(name, value) { ... };
Fruit.Apple = new Fruit("Apple", 0);
Fruit.Pear = new Fruit("Pear", 1);
Fruit.Orange = new Fruit("Orange", 2);

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:

Slice

enum Fruit { Apple, Pear = 3, Orange };

The generated code changes accordingly:

JavaScript

var Fruit = function(name, value) { ... };
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:

JavaScript

var f1 = Fruit.Apple;
var 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;
}
 
var 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).

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