Point Inside Polygon

pip_example.js

var data = {
    polygon: [[0,0], [0,2], [1,3], [2,1], [3,2], [4,0], [3,1], [2,0], [1,1]],
    a: [2, 2],
    b: [1, 2]
};

function pointInPolygon(polygon, point) {
    var len = polygon.length,
        x = point[0], y = point[1],
        j = len - 1, i = 0, c = 0;
    
    for (i, j; i < len; j = i++) {
        y_st = (polygon[i][1] <= y && y < polygon[j][1]) || (polygon[j][1] <= y && y < polygon[i][1]);
        x_st = x < (polygon[j][0] - polygon[i][0]) * (y - polygon[i][1]) / (polygon[j][1] - polygon[i][1]) + polygon[i][0];
        if (y_st && x_st) c = !c;   
    }
    return c;
}

document.write(pointInPolygon(data.polygon, data.b));