JavaScript Mapping for Classes

Class Mapping

A Slice class is mapped to a JavaScript class with the same name. For each Slice field, the JavaScript instance contains a corresponding field (just as for structures and exceptions). Consider the following class definition:

SLICE

class TimeOfDay
{
    short hour;         // 0 - 23
    short minute;       // 0 - 59
    short second;       // 0 - 59
    string tz;          // e.g. GMT, PST, EDT...
}

The Slice compiler generates the following code for this definition:

JS

// JavaScript generated code.
class TimeOfDay extends Ice.Value {
    constructor(hour = 0, minute = 0, second = 0, tz = "") {
        super();
        this.hour = hour;
        this.minute = minute;
        this.second = second;
        this.tz = tz;
    }
}

TYPESCRIPT

// TypeScript generated definition.
class TimeOfDay extends Ice.Value {
    constructor(hour?: number, minute?: number, second?: number, tz?: string);
  
    hour: number;
    minute: number;
    second: number;
    tz: string;
}

There are a number of things to note about the generated code:

The generated TimeOfDay class inherits from Ice.Value.
The generated class provides a constructor that accepts a value for each field.
The generated class defines a JavaScript field for each Slice field.

Generated Constructor

The generated constructor has one parameter for each field. This allows you to construct and initialize an instance in a single statement (instead of first having to construct the instance and then assign to its fields).

For example:

JS

const tod = new TimeOfDayI(14, 45, 00, "PST"); // 14:45pm PST

All these parameters have also default values (see Fields).

For derived classes, the constructor requires an argument for every field of the class, including inherited fields. For example, consider the the definition from Class Inheritance once more:

SLICE

class TimeOfDay
{
    short hour;         // 0 - 23
    short minute;       // 0 - 59
    short second;       // 0 - 59
    string tz;          // e.g. GMT, PST, EDT...
}

class DateTime extends TimeOfDay
{
    short day;          // 1 - 31
    short month;        // 1 - 12
    short year;         // 1753 onwards
}

The constructors generated for these classes are similar to the following:

JS

class DateTime extends TimeOfDay {
    constructor(hour, minute, second, tz, day = 0, month = 0, year = 0) {
        super(hour, minute, second, tz);
        this.day = day;
        this.month = month;
        this.year = year;
    }
}

TypeScript

TYPESCRIPT

class DateTime extends TimeOfDay {
    constructor(
          hour?: number, 
          minute?: number, 
          second?: number, 
          tz?: string, 
          day?: number, 
          month?: number, 
          year?: number);
  
    day: number;
    month: number;
    year: number;
}