Question

How does JavaScript deal with functions with names ending with ()? Consider for example the following piece of code:

var foo() = function () { }; // The empty function

var bar = function(foo) { var myVariable = foo(); };

It seems like there are two possible interpretations for what foo(); means:

1. Execute the argument foo. This assigns myVariable the returned value of foo.
2. Consider foo() as the name of the function defined at first. This assigns myVariable the empty function.

Is this even legal code? If so, what are the rules?

Answer 1

Is this even legal code?

No:

var foo() = function () { }; 

should be:

var foo = function () { }; 

If so, what are the rules?

In this case the foo argument will have precedence because it is defined in an inner scope than the foo function. So it’s really a matter of scope: where is the variable defined. The interpreter first starts by looking in the innermost scope of the code, then in the outer, … until it reaches the global scope (the window object).

So for example the result of the following code will be 123 as seen in this live demo:

var foo = function () { alert('we are in the foo function'); };
var bar = function(foo) { var myVariable = foo(); alert(myVariable); };
bar(function() { return 123; });