When draw a rect with path, fill it, then want the stroke to disappear.
stroke: false,
is the trick.
Set stroke: null
The html5 canvas spec defines that ctx.lineWidth = 0 (object.strokeWidth) must be ignored (uses instead default value 1.0).
http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-linewidth
@Kienz is right. I think this is just HTML5 thing. Refer to here, http://www.w3schools.com/svg/svg_stroking.asp
Most helpful comment
Set
stroke: nullThe html5 canvas spec defines that ctx.lineWidth = 0 (object.strokeWidth) must be ignored (uses instead default value 1.0).
http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-linewidth