Methods and Inheritance
Add typed methods and extend classes with extends and super.
Syntax
class Dog extends Animal { }Class methods are typed functions attached to instances. A class can extend another to inherit its members, calling the parent constructor with super.
Subclasses can add new methods or override existing ones to specialize behavior.
Example
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When to use it
- An Animal base class defines a speak method that is overridden by Dog and Cat subclasses with specific sounds.
- A Shape base class exposes an area method that Rectangle and Circle override with their own typed calculations.
- A service class calls super() in a child constructor to pass required fields to the base class before adding its own.
More examples
Typed method with return
Defines two typed methods on a class that operate on private properties set via constructor shorthand.
class Rectangle {
constructor(
private width: number,
private height: number,
) {}
area(): number {
return this.width * this.height;
}
perimeter(): number {
return 2 * (this.width + this.height);
}
}Inheritance with super
Extends a base class and overrides a method, calling super() in the child constructor to initialise the base fields.
class Animal {
constructor(public name: string) {}
speak(): string {
return `${this.name} makes a sound.`;
}
}
class Dog extends Animal {
constructor(name: string, public breed: string) {
super(name);
}
speak(): string {
return `${this.name} barks!`;
}
}Method calling super method
Overrides a method and calls super.log() to reuse the parent implementation with additional behaviour.
class Logger {
log(message: string): void {
console.log(`[LOG] ${message}`);
}
}
class TimestampLogger extends Logger {
log(message: string): void {
super.log(`[${new Date().toISOString()}] ${message}`);
}
}
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