求 ie下使用excanvas使canvas兼容IE的错误解决方案

报错出 var cxt = canva.getContext("2d");
没掉用excanvas.js里的方法js代码 function createLine(x1, y1, x2, y2,domNa) {       
             var canva = document.getElementById("" + domNa + "");
                var cxt = canva.getContext("2d");
                cxt.strokeStyle = '#f00';
                cxt.moveTo(x1, y1); //起点
                cxt.lineTo(x2, y2); //终点
                cxt.stroke();
            }
            $(document).ready(
                function() {
                    debugger;
                    var writeline = $("canvas");
                    for (var i = 0; i < writeline.length; i++) {
                        var line = writeline[i].id;
                        var sline= new Array();
                        sline=line.split('-');
                        createLine(sline[0],sline[1],sline[2],sline[3],line);
                    }                }
            );
  Literal2.Text += "<canvas id='" + level * 100 + "-" + nowCount * 100 + "-" + (level + 1) * 100 + "-" + newCount * 100 + "'></canvas>";