How is it possible for Typescript to let me create an object without explicitly defining all mandatory fields?

After creating a class and instantiating an object from it through the constructor, I expected to receive an error message indicating missing properties. However, despite the fact that the class description specified required fields, I was able to create an object without including them explicitly, and no errors were thrown. Strangely, when attempting to create an object using "const toyota: Vehicle = {}", an error did occur. Why is this discrepancy happening?

class Vehicle {
  isSpecial: boolean;
  wheels: number;
  brand: string;
   model: string;
   mileage: number;
   isUsed: boolean;
   constructor (wheels: number, mileage: number) {
     this.wheels = wheels;
     this.mileage = mileage;
   }
   drive(): void {
     this.mileage += 100;
   };
 }

 const toyota: Vehicle = new Vehicle(4, 200);

 console.log(toyota);

Expected: error "Type '{}' is missing the following properties from type 'Vehicle': isSpecial, brand, model, and 2 more." Actual: no errors, object created

Answer №1

To activate the --strictPropertyInitialization option in the compiler, you will receive notifications here. This setting will help in identifying uninitialized properties and displaying errors highlighting uninitialized properties can be activated here.

Answer №2

  hasSpecialFeature: boolean;
  numberOfWheels: number;
  brandName: string;
   carModel: string;
   totalMileage: number;
   usedBefore: boolean;

These are not mandatory declarations, but rather options that you have access to. Not every instance variable within this needs to be declared in the constructor. Typescript does not enforce their declaration within the constructor function. The only required elements are the ones specified as arguments in your constructor function.

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