Find line-line and polygon-line intersection

intersection.ts

function Intersection(status) {
    if ( arguments.length > 0 ) {
        this.init(status);
    }
}


/*****
*
*   init
*
*****/
Intersection.prototype.init = function(status) {
    this.status = status;
    this.points = new Array();
};


/*****
*
*   appendPoint
*
*****/
Intersection.prototype.appendPoint = function(point) {
    this.points.push(point);
};


/*****
*
*   appendPoints
*
*****/
Intersection.prototype.appendPoints = function(points) {
    this.points = this.points.concat(points);
};


Intersection.intersectLineLine = function(a1, a2, b1, b2) {
    var result;
    
    var ua_t = (b2.x - b1.x) * (a1.y - b1.y) - (b2.y - b1.y) * (a1.x - b1.x);
    var ub_t = (a2.x - a1.x) * (a1.y - b1.y) - (a2.y - a1.y) * (a1.x - b1.x);
    var u_b  = (b2.y - b1.y) * (a2.x - a1.x) - (b2.x - b1.x) * (a2.y - a1.y);

    if ( u_b != 0 ) {
        var ua = ua_t / u_b;
        var ub = ub_t / u_b;

        if ( 0 <= ua && ua <= 1 && 0 <= ub && ub <= 1 ) {
            result = new Intersection("Intersection");
            result.points.push(
                  [
                    a1.x + ua * (a2.x - a1.x),
                    a1.y + ua * (a2.y - a1.y)
                  ]
                );
        } else {
            result = new Intersection("No Intersection");
        }
    } else {
        if ( ua_t == 0 || ub_t == 0 ) {
            result = new Intersection("Coincident");
        } else {
            result = new Intersection("Parallel");
        }
    }

    return result;
};


Intersection.intersectLinePolygon = function(a1, a2, points) {
    var result = new Intersection("No Intersection");
    var length = points.length;

    for ( var i = 0; i < length; i++ ) {
        var b1 = points[i];
        var b2 = points[(i+1) % length];
        var inter = Intersection.intersectLineLine(a1, a2, b1, b2);

        result.appendPoints(inter.points);
    }

    if ( result.points.length > 0 ) result.status = "Intersection";

    return result;
};

Soure: http://www.kevlindev.com/gui/math/intersection/