entity.js

// The game is composed of entities

function Entity() {
  // A game entity has ...

  // A position
  this.x = 0
  this.y = 0

  // Dimensions
  this.width = 0
  this.height = 0

  // A velocity: speed with direction
  this.xVelocity = 0
  this.yVelocity = 0
}

// On each update, we apply the velocity to the current position.
// This makes the entity move.
// Entities are expected to override this method.
Entity.prototype.update = function() {
  this.x += this.xVelocity
  this.y += this.yVelocity
}

// The entity knows how to draw itself.
// All entities of our game will be white rectangles.
Entity.prototype.draw = function(context) {
  context.fillStyle = '#fff'
  context.fillRect(this.x, this.y, this.width, this.height)
}

// Basic bounding box collision detection.
// Returns `true` if the entity intersect with another one.
Entity.prototype.intersect = function(other) {
  return this.y + this.height > other.y &&
         this.y               < other.y + other.height &&
         this.x + this.width  > other.x &&
         this.x               < other.x + other.width
}