Intro to JavaScript Classes Constructor Functions

Learning objective: By the end of this lesson, students will understand how to use constructor functions in place of the class keyword.

What are constructor functions?

Before classes arrived via ES2015, constructor functions were used in place of classes. They accomplished the same task with a now outdated syntax.

Code written today will most likely use the class keyword, but you may encounter older code using constructor functions.

Let’s look at how the Car class can be written as a constructor function:

function Car(make, model, color) {
  this.make = make;
  this.model = model;
  this.color = color;
  this.isRunning = false;  // default to false
};

Car.prototype.start = function() {
  this.isRunning = true;
  console.log('Running!');
};

// other prototype (instance) methods defined like above would go here
	
// Instantiation is identical
const car = new Car('Toyota', 'Camry', 'Green')

Static methods would be created directly on the constructor function:

Car.about = function() {
  console.log('I\'m the Car class!');
};