Editing Tail call (section)

==Syntactic form==
A tail call can be located just before the syntactical end of a function:

<syntaxhighlight lang="javascript">
function foo(data) {
    a(data);
    return b(data);
}
</syntaxhighlight>

Here, both <code>a(data)</code> and <code>b(data)</code> are calls, but <code>b</code> is the last thing the procedure executes before returning and is thus in tail position. However, not all tail calls are necessarily located at the syntactical end of a subroutine:

<syntaxhighlight lang="javascript">
function bar(data) {
    if (a(data)) {
        return b(data);
    }
    return c(data);
}
</syntaxhighlight>

Here, both calls to <code>b</code> and <code>c</code> are in tail position. This is because each of them lies in the end of if-branch respectively, even though the first one is not syntactically at the end of <code>bar</code>'s body.

In this code:

<syntaxhighlight lang="javascript">
function foo1(data) {
    return a(data) + 1;
}
</syntaxhighlight>
<syntaxhighlight lang="javascript">
function foo2(data) {
    var ret = a(data);
    return ret;
}
</syntaxhighlight>
<syntaxhighlight lang="javascript">
function foo3(data) {
    var ret = a(data);
    return (ret == 0) ? 1 : ret;
}
</syntaxhighlight>

the call to <code>a(data)</code> is in tail position in <code>foo2</code>, but it is '''not''' in tail position either in <code>foo1</code> or in <code>foo3</code>, because control must return to the caller to allow it to inspect or modify the return value before returning it.