Proper way to call superclass functions from subclass

You can write it like this :

SuperClass.prototype.printInfo = function(){
  console.log("printing from superclass printInfo");
  console.log(this.info); 
};

SubClass.prototype.printInfo = function(){
  console.log("calling superclass");
  SuperClass.prototype.printInfo.call(this);
  console.log("called superclass");
};

class Thing {
  constructor(age) { this.age = age; }
  die(how) { console.log(`Died of ${how}`); }
}

class Me extends Thing {
  constructor() { super(59); console.log(`I am ${this.age}`); }
  // Refer to a method from the superclass that is overridden in the subclass
  die(how) { super.die('liver failure'); console.log(`while ${how}`) }
}

(new Me()).die('hang gliding');

You are messing with the SubClass's prototype with the SuperClass's object, in this line

SubClass.prototype = new SuperClass();

the child's prototype should depend on the Parent's prototype. So, you can inherit like this

SubClass.prototype = Object.create(SuperClass.prototype);

Also, it is quite normal to change the constructor to the actual function, like this

SubClass.prototype.constructor = SubClass;

To keep your implementation generic, you can use Object.getPrototypeOf, to get the parent prototype in the inheritance chain and then invoke printInfo, like this

SubClass.prototype.printInfo = function() {
    Object.getPrototypeOf(SubClass.prototype).printInfo(this);
};

Since, info is defined in the SubClass yet, it will print undefined. You might also want to call the parent't constructor, like this

var SubClass = function() {
    SuperClass.call(this);
};

Note: You are creating global variables, by omitting var keyword before SuperClass and SubClass.

After reading all the answers, I am using the following inheritance mechanism:

var SuperClass = function()
{
    this.info = "I am superclass";
    console.log("SuperClass:");
};

SuperClass.prototype.printInfo = function()
{
    console.log("printing from superclass printInfo");
    console.log("printinfo");
    console.log(this.info);
};

var SubClass = function(){
    SuperClass.call(this);
};

SubClass.prototype = Object.create(SuperClass.prototype);
SubClass.prototype.constructor = SubClass;

SubClass.prototype.printInfo = function()
{
    console.log("calling superclass");
    Object.getPrototypeOf(SubClass.prototype).printInfo.call(this);
    console.log("called superclass");
};

var sc = new SubClass();
sc.printInfo();