[]为什么调用封装的原生画线api不显示？

function drawLine(layaCvs,startX,startY,toX,toY,lineWidth,strokeStyle,lineCap)

{

	var layaCanvas = layaCvs;

	var oContext = layaCanvas.getContext("2d");

	

	oContext.beginPath();

	oContext.moveTo(startX, startY);

	oContext.lineTo(toX, toY);

	oContext.lineWidth = lineWidth;

	oContext.strokeStyle = strokeStyle;

	oContext.lineCap = lineCap;     //自定义线帽

    oContext.stroke();

}

var canvas:* = Browser.canvas;

__JS__("drawLine(canvas, 0, 0, 300, 300, 15, '#ff0000','round')");