Guaranteed Instances

example.js

var Car = function(make, model, color) {
  this.make = make;
  this.model = model;
  this.color = color;
};

// This way works:
var pinto = new Car('ford', 'pinto', 'green');
// but this doesn't:
var pinto = Car('ford', 'pinto', 'green');

// Possible Solution:
var Car = function(make, model, color) {
  if (!(this instanceof Car)) {
    return new Car(make, model, color);
  }

  this.make = make;
  this.model = model;
  this.color = color;
};

// Sometimes I like to write it this way:
var Car = function fn(make, model, color) {
  if (!(this instanceof fn)) {
    return new fn(make, model, color);
  }

  this.make = make;
  this.model = model;
  this.color = color;
};

// Now both ways work:
var pinto = new Car('ford', 'pinto', 'green');
var pinto = Car('ford', 'pinto', 'green');