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Asked: 2026-06-12T18:14:03+00:00

I have a class named BMW defined in BMW.ts as follows: ///<reference path=../Thing.ts/> module

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I have a class named BMW defined in BMW.ts as follows: 

///<reference path="../Thing.ts"/>

module Entities.Cars {

    import e = Entities;

    export class BMW extends Vehicle {

        public series: string;

         constructor ( model : string, series : string) {
            super("BMW", model)
            this.series = series;
        }

         drive() {
             alert("driving a bimmer is a different kind of feeling");
         }       

         toString() : string
         { 
             return this.getName() + " " + this.series + " " + this.getType();
         }
    }
}

In another file Thing.ts, I have Vehicle and Thing classes defined as follows:

module Entities {

    // Class
    export class Thing {

        private _name: string;
        private _type: string;

        // Constructor
        constructor (public name: string, public type: string) {
            this._name = name;
            this._type = type;
         }

        getName(): string { return this._name; }
        setName(name: string) { this._name = name; }


        getType(): string { return this._type; }
        setType(name: string) {
            this._type = name;
        }

        toString() : string
        { 
            return "Entities.Thing";        
        }
    }

    export class Vehicle extends Thing {

        public cargoCapacity: number;
        public fuelType: string;
        public owner: string;

        constructor (make: string, model : string) {
            super(make, model)
        }

        drive() {
        }

        toString(): string {
            return "Entities.Vehicle";
        }
    }
}

When I attempt to execute the following code after referencing Thing and BMW TypeScript files:

var car = new Entities.Cars.BMW("335i", "E90");
car.drive();

I get an exception with the following error ” Microsoft JScript runtime error: Unable to get value of the property ‘BMW’: object is null or undefined”. The generated Javascript for BMW has an error. What is wrong with my above snippet?

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1 Answer

  1. Editorial Team

    There is nothing wrong with your code so it seems like your import order for the generated javascript files is wrong. The specification says the following:

    Initialization order of the source files that make up the global module ultimately depends on the order in which the generated JavaScript files are loaded at run-time (which, for example, may be controlled by tags that reference the generated JavaScript files).

    I have generated a file app.ts as follows:

    ///<reference path='Things.ts'/>
///<reference path='bmw/BMW.ts'/>
var car = new Entities.Cars.BMW("335i", "E90");
car.drive();

    At this point you have two options:

    1. Let the compiler determine the correct order for executing the files by generating a single output file

      tsc --out app.js app.ts

      Then you only have to source app.js.

    2. Specify the correct order manually. For me, the following is the only order that works without throwing errors.

      <html>
    <head>
        <script src="Things.js"></script>
        <script src="bmw/BMW.js"></script>
        <script src="app.js"></script>
    </head>
    <body>
    </body>
</html>
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