shorter way to run functions using its variables - php

Question

js
var a = 'sun';
var b = 'earth';
var fn = 'some_fn';
$.post('index-pro.php', {fn, a, b}, function(data){
console.log(data);
});
I have a lot of code parts like the above, using different variables, but always refering to index-pro.php as a target file.
index-pro.php
if(isset($_POST)){extract($_POST);}
if(isset($fn) && $fn == 'some_fn'){some_fn($a, $b);}
elseif(isset($fn) && $fn == 'another_fn'){another_fn($another_vars);}
elseif(isset($fn) && $fn == 'another_fn'){another_fn($another_vars);}
How can I say something like this:
whatever fn is set -> run this fn using its variables.

Answer 1

You can call function using not only it's name, but even by a variable, which stores function name:
$fn = 'doStuff';
$a = 2;
$fn($a);
function doStuff($arg) {
echo $arg;
}
If your arguments are different for different functions then I advise to post data as two items: funcName and funcArguments, for example:
$.post('index-pro.php', {funcName: fn, funcArguments: [a, b]}, function(data){
console.log(data);
});
On server side you can do something like (I skip checks and other stuff, just baseline):
$fn = $_POST['funcName'];
$arguments = $_POST['funcArguments'];
// with php5.6/php7 you have variadic `...` syntax
$fn(...$arguments);
// or use plain old `call_user_func_array`:
call_user_func_array($fn, $arguments);

Answer 2

That's what you need. Simple idea: provide an array with arguments to a function name: http://php.net/manual/de/function.call-user-func.php
I didn't tried it out, but this should work:
JS
var a = 'sun';
var b = 'earth';
var fn = 'some_fn';
$.post('index-pro.php', {function: fn, args: [a, b]}, function(data){
console.log(data);
});
PHP
$functionName = $_POST['function'];
$args = $_POST['args'];
call_user_func ($functionName,$args)