Instant HTML5 2D Platformer - Instant HTML5 2D Platformer - page 10

this.left = true;

if (key.keyCode == 39 || key.keyCode == 68)
this.right = true;
}

this.keyUp = function(key) {

if (key.keyCode == 38 || key.keyCode == 87)
this.up = false;

if (key.keyCode == 40 || key.keyCode == 83)
this.down = false;

if (key.keyCode == 37 || key.keyCode == 65)
this.left = false;

if (key.keyCode == 39 || key.keyCode == 68)
this.right = false;
}

4. Each of these functions performs a number of checks to determine whether a key

has been pressed or released. As a result these checks determine in which direction
the player should move if a certain key has been pressed.

5. In order to move the player in the direction in question, we must update the number

of units the player has moved each frame by introducing an Update function to the
player object as follows:
this.Update = function (deltaTime, context, deltaX, deltaY) {

if(this.up)
this.y -= this.velocity * deltaTime;

if(this.down)
this.y += this.velocity * deltaTime;

if (this.left)
this.x -= this.velocity * deltaTime;

if (this.right)
this.x += this.velocity * deltaTime;
}