JavaScript Changing class method from outside

Question

Is it possible in JavaScript to change a method of a class from outside?
Example:

class Sub {
constructor (num) {
this.num = num;
}
substraction(n) {
return this.num - n;
}
}

can I add, for example, console.log() to every call of substraction() without changing class Sub?

Answer 1

You can extend the class and override the method. There are other ways, but IMO this is the most straight forward and easy to understand.

class Sub {
constructor(num) {
this.num = num;
}
subtraction(n) {
return this.num - n;
}
}

class Sub2 extends Sub {
subtraction(n) {
console.log(this.num - n);
}
}

let sub = new Sub2(6);
sub.subtraction(4); // outputs 2 in the console