javascript game help

[giliagmon]

im working on a javascript game and i don't want the player to be able to leave the canvas. i have made it where you can't leave the bottom or right side like this

this.hitBottom = function(){
        var rockbottom = myGameArea.canvas.height - this.height;
        var rockside = myGameArea.canvas.width - this.width;
        if (this.y > rockbottom) {
            this.y = rockbottom;
            }
            if(this.x > rockside){
              this.x = rockside;
            }

but i can't figure out how to do the other 2 sides

[LUUD18]

Bigger then 0?

 

Or otherwise get the with/height of the canvas and do:

rockbottom-height : Would give you the upper border.

rockside-width: Would give you the left border.