Question

I am looking at this function

function foo(x) {
  var tmp = 3;
  return function (y) {
    alert(x + y + (++tmp));
  }
}
var bar = foo(2); // bar is now a closure.
bar(10);

when I run it, the variables get the following values

x = 2,
y = 10
tmp = 3.

Now I see that in foo(2) x is passed as 2. So its understandable that x is getting the value of 2. But then bar(10) is assigning a value of 0 to y. Hows that? I am confused on how does the receiving function know that 10 is the value for y assigned by bar(10)

Answer 1

foo(2) returns an anonymous function which accepts one parameter (y). As you’re setting bar to be the return value of foo(2), bar becomes a reference to that anonymous function.

So, when you call bar(10) you’re calling the anonymous function foo returns, and so 10 is being set to the parameter y.