Edit in JSFiddle

function findLineCollication(x1, y1, x2, y2, x3, y3, x4, y4){
    var a1 = y2-y1;
    var b1 = x1-x2;
    var c1 = a1*x1 + b1*y1;
    var a2 = y4-y3;
    var b2 = x3-x4;
    var c2 = a2*x3 + b2*y3;
    var det = a1*b2-a2*b1;
    if(det != 0){
       var x = (b2*c1 - b1*c2)/det;
       var y = (a1*c2 - a2*c1)/det;
       if(x >= Math.min(x1, x2) && x <= Math.max(x1, x2) 
          && x >= Math.min(x3, x4) && x <= Math.max(x3, x4)
          && y >= Math.min(y1, y2) && y <= Math.max(y1, y2) 
          && y >= Math.min(y3, y4) && y <= Math.max(y3, y4)){     
          writeSVG(x, y);
          return "x:" + x + " <br /> y: " + y;
       }   
    }
    return "No collication";
}

function writeSVG(x, y){
document.getElementById("lines").innerHTML += "<circle cx=\""+x+"\" cy=\""+y+"\" r=\"5\" fill=\"green\" />";  
document.getElementById("lines").innerHTML += "<text x=\"" + (x1-10) + "\" y=\"" + (y1-10) + "\" fill=\"red\">x1, y1</text>";
document.getElementById("lines").innerHTML += "<text x=\"" + (x2-10) + "\" y=\"" + (y2+20) + "\" fill=\"red\">x2, y2</text>";
document.getElementById("lines").innerHTML += "<text x=\"" + (x3-10) + "\" y=\"" + (y3+20) + "\" fill=\"black\">x3, y3</text>";
document.getElementById("lines").innerHTML += "<text x=\"" + (x4-10) + "\" y=\"" + (y4-10) + "\" fill=\"black\">x4, y4</text>";
document.getElementById("lines").innerHTML += "<text x=\"" + (x+15) + "\" y=\"" + (y+10) + "\" fill=\"green\">x, y</text>";

document.getElementById("lines").innerHTML += "<circle cx=\"" + x1 + "\" cy=\"" + y1 + "\" r=\"5\" fill=\"red\" />";
document.getElementById("lines").innerHTML += "<circle cx=\"" + x2 + "\" cy=\"" + y2 + "\" r=\"5\" fill=\"red\" />";
document.getElementById("lines").innerHTML += "<circle cx=\"" + x3 + "\" cy=\"" + y3 + "\" r=\"5\" fill=\"black\" />";
document.getElementById("lines").innerHTML += "<circle cx=\"" + x4 + "\" cy=\"" + y4 + "\" r=\"5\" fill=\"black\" />";
}


var x1 = document.getElementById("Line1").x1.baseVal.value;
var y1 = document.getElementById("Line1").y1.baseVal.value;
var x2 = document.getElementById("Line1").x2.baseVal.value;
var y2 = document.getElementById("Line1").y2.baseVal.value;
var x3 = document.getElementById("Line2").x1.baseVal.value;
var y3 = document.getElementById("Line2").y1.baseVal.value;
var x4 = document.getElementById("Line2").x2.baseVal.value;
var y4 = document.getElementById("Line2").y2.baseVal.value;
var sonuc = findLineCollication(x1, y1, x2, y2, x3, y3, x4, y4);

document.getElementById("sonuc").innerHTML += sonuc;
<div id="sonuc">
</div>
<svg id="lines" height="300" width="700">
 <line id="Line1" x1="30" y1="30" x2="200" y2="200" style="stroke:red;stroke-width:2" />
 <line id="Line2" x1="10" y1="100" x2="300" y2="50" style="stroke:black;stroke-width:2" />
</svg>