Question

I have the following code from a javascript book and the callback seems to be passed an expression as an argument. Is that the case or am I seeing this wrong? I didnt know, even though it works, that that was possible.

function multiplybytwo(a,b,c,callback)  {
  var i, ar =[];
  for(i=0;i<3;i++)  
  {
    ar[i] = callback(arguments[i]*2);  
  }
  return ar;  
}  

function addone(a)  {
  return a+1;  
} 

myarr =multiplybytwo(1,2,3,addone);

Answer 1

callback(arguments[i]*2); 

is equivalent to

var a = arguments[i]*2;
callback(a);

Same as callback(1+2); to callback(3);