var PointPrototype={
  x:0,
  y:0,
  print:function(){
    console.log('x:'+this.x+',y:'+this.y)
  }
}

p0=Object.create(PointPrototype,{
  x:{value:5},
})

p0.print() //x:5,y:0

var LinePrototype=Object.assign(PointPrototype,{
  m:0,
  print:function(){
    console.log(this.m?'y='+this.m+"x+"+(this.y-(this.m*this.x)):'y='+(this.y-this.m*this.x))
  }
})

l0=Object.create(LinePrototype,{
  y:{value:2},
  m:{value:5}
});

l0.print() //y=5x+2