SOURCE

//参数传递
//ECMA中所有函数的参数都是按值传递的
function test1(){
  var bb = 1;
  function aa(bb) {
      bb = 2;
      alert(bb);
  };
  aa(bb);
  alert(bb);
}

//非参传递
function test2(){
  var bb = 1;
  function aa() {
      bb = 2;
      alert(bb);
  };
  aa(bb);
  alert(bb);
}

//XX传递
function test3(){
  var bb = 1;
  function aa(num) {
      bb = 2;
      alert(bb);
  };
  aa(bb);
  alert(bb);
}

var xxx="global";  
if(true){  
    var xxx="local";  
   alert(xxx);
}  
alert(xxx);

<h1>
  <a href="https://www.nowcoder.com/questionTerminal/8e3f169e6199429cb730fe3cd40957b0?mutiTagIds=644&orderByHotValue=1">牛客刷题
  </a>
</h1>
<button type="button" onclick="test1()">参数传递</button>
<p id="test1"></p>
<button type="button" onclick="test2()">非参传递</button>
<p id="test2"></p>
<button type="button" onclick="test3()">XX传递</button>
<p id="test2"></p>