一道JS作用域的面试题，求解

var x = 0
function foo(x=1,y=function() {
  x=2
  console.log(x);
}) {
  console.log(x);
  var x=0
  console.log(x);
  y()
  console.log(x);
}
foo()
console.log(x);
//输出为
//1
//0
//2
//0
//0