How to use Constructor Property In Javascript
Each JavaScript object has a constructor property which refers to the constructor function that created it. By comparing the constructor property of an object with a specific constructor function, you can identify the type of the object. This method provides a direct way to check the constructor function of an object and can be useful in certain scenarios.
Syntax:
if (object.constructor === DerivedClass) {
// Process object as DerivedClass
}
Example: The below example will explain the use of constructor property tonarrow a type of derived class.
Javascript
interface Shape { draw(): void;}class Circle implements Shape { draw() { console.log("Drawing a circle"); }}class Rectangle implements Shape { draw() { console.log("Drawing a rectangle"); }}const shapes: Shape[] = [new Circle(), new Rectangle(), new Circle()];for (const shape of shapes) { if (shape.constructor === Circle) { console.log("Circle instance found"); (shape as Circle).draw(); } else if (shape.constructor === Rectangle) { console.log("Rectangle instance found"); (shape as Rectangle).draw(); }} |
Output:
Circle instance found
Drawing a circle
Rectangle instance found
Drawing a rectangle
Circle instance found
Drawing a circle
How to Narrow a Type of Derived Class Instances while Processing an Array ?
When it comes to JavaScript arrays that contain derived class instances, narrowing down the types is a must to access the specific functions or properties that are unique to those derived classes. Narrowing encompasses an act of specifically type-checking and casting objects explicitly to their derived types.
Table of Content
- Using instanceof Operator
- Using Constructor Property
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