Javascript closures vs PHP closures, what's the difference?

They do pretty much work the same way. Here's more information about the PHP implementation: http://php.net/manual/en/functions.anonymous.php

You can use a closure (in PHP called 'anonymous function') as a callback:

// return array of ids
return array_map( function( $a ) { return $a['item_id']; }, $items_arr );

and assign it to a variable:

$greet = function( $string ) { echo 'Hello ' . $string; }; // note the ; !
echo $greet('Rijk'); // "Hello Rijk"

Furthermore, anonymous function 'inherit' the scope in which they were defined - just as the JS implementation, with one gotcha: you have to list all variables you want to inherit in a use():

function normalFunction( $parameter ) {
    $anonymous = function() use( $parameter ) { /* ... */ };
}

and as a reference if you want to modify the orignal variable.

function normalFunction( $parameter ) {
    $anonymous = function() use( &$parameter ) { $parameter ++ };
    $anonymous();
    $parameter; // will be + 1
}