The extends keyword is used in class declarations/expressions to create a class which is a child of another class. It can be used to subclass custom classes as well as built-in objects. The syntax would be as below,
1 | class ChildClass extends ParentClass { ... } |
Let’s take an example of Square subclass from Polygon parent class,
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | class Square extends Rectangle { constructor(length) { super(length, length); this.name = 'Square'; } get area() { return this.width * this.height; } set area(value) { this.area = value; } } |
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