javascript - Box2dWeb call function when objects collide -

i'm new javascript , box2d, wondering if knows how can call custom function when 2 objects collide. tried using examples uses b2contactlistener without succes. i've placed object above , let standard box2d physics it's thing.

i recieve 2 console outputs, first null , second ball following code:

var listener = new box2d.dynamics.b2contactlistener; listener.begincontact = function(contact) {     console.log(contact.getfixturea().getbody().getuserdata());      console.log(contact.getfixtureb().getbody().getuserdata()); };.  

the 2 objects need collide b2_dynamicbody (ball) , b2polygonshape. (rectangle). using bodydef.userdata = "ball"; in ball.js , bodydef.userdata = "mouse"; in mouse.js try identify if hit. instead ball displayed.

next i'm sure not correct way detecting collision :p hope i've explained enough, steer me in right direction?

ok solved myself, apparently had add custom event world create box2d. so, issue solved me reading big chunks of box2d documentation/manual can found here:

i started adding string userdata() every object can collide , has else next colliding. using following code:

bodydef.userdata = "car"; 

note: every object has have it's own unique string.

then created new contact listener (formulated in question above) , listened fixtures colliding each other. when happens, 'save' fixtures userdata() in variables can use objects collide each other.

var contactlistener = new box2d.dynamics.b2contactlistener; contactlistener.begincontact = function(contact) {      var fixa = contact.getfixturea().getbody().getuserdata();     var fixb = contact.getfixtureb().getbody().getuserdata();      // if else statement here...  };  world.setcontactlistener(contactlistener); 

finally, added last statement world.setcontactlistener(contactlistener); add event world, making possible listen collisions, forgot add , problem.

hope finds usefull!