Learning exercise about "this" scoping and real javascript OO. Pay particular attention to this.bbox and it's use

CharacterElement.js

var CharacterElement = function(locChar) {
	this.x = null;
	this.y = null;
	this.width = null;
	this.dy = null;
	this.value = (locChar !== null) ? locChar : "";
	this.se_newline = "";
	this.characterAttribute = null;
	this.bbox = null;
		
	this.setBBox = function( charAttr ) {
		// precompute the bounding box coordinates for the 
		// character
		this.bbox = {
					ul: {
						x: this.x,
						y: this.y + (charAttr.attr.font_size * charAttr.attr.leading) + (charAttr.attr.font_size * charAttr.attr.ascent)
					},
					ur: {
						x: this.x + this.width,
						y: this.y + (charAttr.attr.font_size * charAttr.attr.ascent)
					},
					ll: {
						x: this.x,
						y: this.y - (charAttr.attr.font_size * charAttr.attr.descent)
					},
					lr: {
						x: this.x + this.width,
						y: this.y - (charAttr.attr.font_size * charAttr.attr.descent)
					}
		};

	};

};