Check if a 2D point is inside 2D simple polygon. It works with convex and concave polygons.

ray-casting.js

function ray_casting(point, polygon){
    var n=polygon.length,
        is_in=false,
        x=point[0],
        y=point[1],
        x1,x2,y1,y2;

    for(var i=0; i < n-1; ++i){
        x1=polygon[i][0];
        x2=polygon[i+1][0];
        y1=polygon[i][1];
        y2=polygon[i+1][1];

        if(y < y1 != y < y2 && x < (x2-x1) * (y-y1) / (y2-y1) + x1){
            is_in=!is_in;
        }
    }

    return is_in;
}

I've noticed that the edge between point[n-1] and point[0] is not taken into account. Please check this fixed version:

function rayCasting(point, polygon) {
    const n = polygon.length
    let isIn = false
    const x = point[0]
    const y = point[1]
    let x1, x2, y1, y2

    x1 = polygon[n-1][0]
    y1 = polygon[n-1][1]

    for (let i = 0; i < n; ++i) {
        x2 = polygon[i][0];
        y2 = polygon[i][1];

        if (y < y1 !== y < y2 && x < (x2 - x1) * (y - y1) / (y2 - y1) + x1) {
            isIn = !isIn;
        }
        x1 = x2
        y1 = y2
    }

    return isIn;
}

Best regards! Tamás

You shouldn't ever write a code anymore. I tried yours and bardi-entel's and they don't work as they should.

You shouldn't ever write a code anymore. I tried yours and bardi-entel's and they don't work as they should.

Your parents shouldn't ever have had you, but here you are, making pointless comments.