Question

  var foo = {
    bar: function() { return this.baz; },
    baz: 1
  };
  (function(){
    return typeof arguments[0]();
  })(foo.bar);

Why does this code return undefined?

I would assume arguments[0] would hold the foo.bar, which is a function. When invoked via arguments[0]() it should return the result of the function evaluation in, this case 1. Hence, typeof arguments[0]() should return “Number” (like typeof 1). Instead, it returns undefined. Why?

Answer 1

this refer to bar function itself.

var foo = {
    bar: function() {return foo.baz; },
    baz:1
  };
  (function(){
    return typeof arguments[0]();
  })(foo.bar);

fiddle : http://jsfiddle.net/W9Jqb/