美团面试-canvas实现放射图

一个nice的面试官对面试经验匮乏者的温暖To snow peak，哈哈

drawRadial(100, 100, 30, 10)
/**
 *@description
 *用canvas画放射图
 *
 *@params
 *x0、y0原点坐标，r放射图半径，放射图平均角度
 *
 * @author   xp
 */
function drawRadial(x0, y0, r, angle){
    r = r || 10;
    angle = angle || 10;
    var len = 360/angle;
    var radian = 2*Math.PI*angle/360;
    var c=document.getElementById("myCanvas");
    var ctx=c.getContext("2d");
    for (var i=1; i<=len; i++) {
        (function(j){
            setTimeout( function timer() {
                x1 = x0 + r*Math.cos(radian*j)
                y1 = y0 + r*Math.sin(radian*j)
                ctx.beginPath();
                ctx.moveTo(x0,y0);
                ctx.lineTo(x1,y1);
                ctx.stroke();
            }, j*1000 );
        }(i))
    }
}