Error: call super outside of class constructor

I try to call parent method but I get error:

Error: call super outside of class constructor

My example :

class xo{
    cool(x){
        console.log(`parent init${x}`)
    }
}
class boo extends xo{
    cool(val){
        super(val);
        console.log(`child init${x}`)
    }
}

x = new boo;