The function in this example returns `true`

if two line segments are intersecting and `false`

if not.

The example is designed for performance and uses closure to hold working variables

// point object: {x:, y:} // p0 & p1 form one segment, p2 & p3 form the second segment // Returns true if lines segments are intercepting var lineSegmentsIntercept = (function(){ // function as singleton so that closure can be used var v1, v2, v3, cross, u1, u2; // working variable are closed over so they do not need creation // each time the function is called. This gives a significant performance boost. v1 = {x : null, y : null}; // line p0, p1 as vector v2 = {x : null, y : null}; // line p2, p3 as vector v3 = {x : null, y : null}; // the line from p0 to p2 as vector function lineSegmentsIntercept (p0, p1, p2, p3) { v1.x = p1.x - p0.x; // line p0, p1 as vector v1.y = p1.y - p0.y; v2.x = p3.x - p2.x; // line p2, p3 as vector v2.y = p3.y - p2.y; if((cross = v1.x * v2.y - v1.y * v2.x) === 0){ // cross prod 0 if lines parallel return false; // no intercept } v3 = {x : p0.x - p2.x, y : p0.y - p2.y}; // the line from p0 to p2 as vector u2 = (v1.x * v3.y - v1.y * v3.x) / cross; // get unit distance along line p2 p3 // code point B if (u2 >= 0 && u2 <= 1){ // is intercept on line p2, p3 u1 = (v2.x * v3.y - v2.y * v3.x) / cross; // get unit distance on line p0, p1; // code point A return (u1 >= 0 && u1 <= 1); // return true if on line else false. // code point A end } return false; // no intercept; // code point B end } return lineSegmentsIntercept; // return function with closure for optimisation. })();

Usage example

```
var p1 = {x: 100, y: 0}; // line 1
var p2 = {x: 120, y: 200};
var p3 = {x: 0, y: 100}; // line 2
var p4 = {x: 100, y: 120};
var areIntersepting = lineSegmentsIntercept (p1, p2, p3, p4); // true
```

The example is easily modified to return the point of intercept. Replace the code between `code point A`

and `A end`

with

```
if(u1 >= 0 && u1 <= 1){
return {
x : p0.x + v1.x * u1,
y : p0.y + v1.y * u1,
};
}
```

Or if you want to get the intercept point on the lines, ignoring the line segments start and ends replace the code between `code point B`

and `B end`

with

```
return {
x : p2.x + v2.x * u2,
y : p2.y + v2.y * u2,
};
```

Both modifications will return false if there is no intercept or return the point of intercept as `{x : xCoord, y : yCoord}`