Object.create vs new

The following code works when I create my object with the constructor but when I do object.Create it doesn't get initialized properly. functionName is not a function. I have two questions. Why isn't the object.create working ?

How would I organize my code within the same Calculator Function so I could use both new and object.create ?

I know I can add the methods to Calculator.prototype and do Object.create but I was wondering if my code can be changed within the current structure to allow for both ?

//var calc = new Calculator();
var calc = Object.create(Calculator);


function Calculator(){
    this.array = [];
    this.results = 0;

    this.calculate = function(){    
        try{
        results = eval(this.array.join(''));
        this.array = [results];
        return results; 
        }
        catch(error){
            alert('Wrong arguments provided');
            return this.array.join('');
        }
    },

    this.isNumber = function(str){
        return !isNaN(parseFloat(str)) && isFinite(str);
    },

    this.addToOperationsArray = function(str){
        if (this.array.length <= 0 && !this.isNumber(str)){ // Don't add operand before any number.
            return; 
        }

        this.array.push(str);

    },
    this.clearEverything = function(){
        this.array = [];
    }
}

There is no constructor invocation with Object.create.

You can get similar results in a multitude of ways. See if something along these lines helps you:

function Calculator() {
  this.array = [];
  this.results = 0;
}
Calculator.prototype = {
  calculate: function() {
    try {
      results = eval(this.array.join(''));
      this.array = [results];
      return results;
    } catch (error) {
      alert('Wrong arguments provided');
      return this.array.join('');
    }
  },
  isNumber: function(str) {
    return !isNaN(parseFloat(str)) && isFinite(str);
  },
  addToOperationsArray: function(str) {
    if (this.array.length <= 0 && !this.isNumber(str)) { // Don't add operand before any number.
      return;
    }

    this.array.push(str);

  },
  clearEverything: function() {
    this.array = [];
  }
};

// create using 'new'
var calc1 = new Calculator();

// create using 'Object.create'
// the constructor function is not called
// but properties of returned object can be passed to the function, and
// you can control the enumerable, writable, configurable properties
var calc2 = Object.create(Calculator.prototype, {
  'array': {
    value: [],
    enumerable: true
  },
  'results': {
    value: 0,
    enumerable: true
  }
});

// create using 'Object.create'
// and invoke the constructor with 'call',
// explicitly setting 'this'
var calc3 = Object.create(Calculator.prototype);
Calculator.call(calc3);


console.log(calc1);   // Calculator {array: Array[0], results: 0}
console.log(calc2);   // Object {array: Array[0], results: 0}
console.log(calc3);   // Object {array: Array[0], results: 0}