Why does Andrew chain the mouse event methods to the original $canvas.mousedown function?

// This wraps the DOM element "<canvas></canvas>" in a brand new object, with brand new properties and brand new methods that were created/attached by jQuery
// This brand new object is what we're calling a "jQuery object"
var $canvas = $('canvas');

var width = $canvas.attr("width"); // In this case, this would return 800

function Person(firstname, lastname) {
  this.firstName = firstname
  this.lastName = lastname
}

Person.prototype.whoDis = function () {
  // This method returns stuff, so this particular method is not chainable
  return `I am ${this.firstName} ${this.lastName}!`
}

Person.prototype.sayMyNameSayMyName = function () {
  // See, this method just logs stuff; it doesn't return anything
  console.log(this.whoDis())
  console.log(this.whoDis())
  // So we can implement chaining!
  return this // This returns a reference to the current instance of the Person constructor
}

var theDonald2 = new Person('John', 'Miller')

var theDonaldSpokesman = theDonald2
  .sayMyNameSayMyName() // logs "I am John Miller!" twice; returns itself
  .whoDis() // returns "I am John Miller!" — so theDonaldSpokesman variable would contain the value "I am John Miller!"