thisArg is the context that the 'callback' should be called from, or
in other words, what "this" represents when that callback is fired. I
believe you are asking if it is possible to send additional arguments
in to the forEach function, though your example does not accomplish
that. The easiest way to send additional arguments through forEach
without modifying the library is to wrap them in a closure:
var myA, myB, set=paper.set();
set.forEach( (function(a,b){ return function(el, i)
{ el.data("a",a).data("b",b); }; } )( myA, myB ) );
This lets the function fire with myA and myB available within the
function context (as a and b), but also does not leave behind residual
anonymous functions for garbage collector to fight with.
Hope this helps.