php和javascript如何执行嵌套函数的区别

Question

我试图想象 javascript 和 php 如何处理嵌套函数。

重点是：

php :

b(); //CANNOT call b at this point because isn't defined yet

a(); //CAN call a at this point because the interpreter see the declar

b(); //ok now i can call b, because the interpreter see the declaration after a execution

function a(){

    function b(){

        echo "inner";

    }

}

同时在javascript 中：

b(); //CANNOT call b isn't defined yet

a(); //CAN call a at this point because the interpreter see the declar

function a(){

    function b(){

        console.log("inner");

    }

}

a(); //ok now i can call a because is defined

b(); // **CANNOT** call b yet !!   

为什么在 javascript 中即使 a 被执行我也不能调用 b() ？PHP 在哪些方面表现不同？