Question

According to the v8 ticket, it said

Tail call elimination isn’t compatible with JavaScript as it is used in the real
world. Consider the following:

function foo(x) {
  return bar(x + 1);
}

function bar(x) {
  return foo.arguments[0];
}

foo(1)

This returns 1.

It didn’t explain clearly what if JavaScript support tail call, what would be the value of foo(1) and why?

Anyone can explain?

Answer 1

It didn’t explain clearly what if JavaScript support tail call, what
would be the value of foo(1) and why?

The value will be 1 when you do foo(1) because foo function returns the result of bar function and bar function does nothing but read the first argument of foo function with foo.arguments[0] (arguments is implied object available to every function which is used to read arguments passed to function) and return it. The first argument of foo happens to be 1 when you do:

foo(1);

Here is break-down:

function foo(x) {
  return bar(x + 1); // foo calls bar function which returns 1
}

function bar(x) {
  return foo.arguments[0]; // bar reads first argument passed to foo which is 1
}

foo(1); // 1 is x in foo function

The bar function just reads first argument of foo (via foo.arguments[0]) and returns it because of which no addition is done.