var globalEval = eval;     //定义全局eval函数别名
    var a ="global", b = "global";    //全局变量
    function c(){
      var a = "local";      //局部变量
      eval('a+="changed"');  //直接更改局部变量的值
      return a;      //返回更改后的局部变量
    }
    function d(){
      var b = "local";
      globalEval("b+='changed'");
      return b;
    } 
    console.log(c(), a); //localchanged       global
    console.log(d() , b) //local              globalchanged

相关文章：https://blog.csdn.net/wangqing84411433/article/details/70197523