用JS和PHP逃避"+"

var a = 1;
var b = 2;
var c = a + b; // c的值为3

$a = 1;
$b = 2;
$c = $a + $b; // $c的值为3

var a = "Hello";
var b = "World";
var c = a + " " + b; // c的值为"Hello World"

$a = "Hello";
$b = "World";
$c = $a . " " . $b; // $c的值为"Hello World"