var val = 12; function fun1(){ console. log(val); var val = 20; console.log(val); } fun1();
var val = 12; function fun1(){ console. log(val); // 函数声明提升 var val = 20; console.log(val); } fun1();
var val = 12; function fun1(){ var val; console.log(val); //为赋值undefined val = 20; //在原位置对变量进行赋值操作 console.log(val); //输出20 } fun1();
var val =12;function fun1(){var val;console. log(val);val =20;console.log(val);}fun1();
function fun1(){ var val console. log(val); val = 20; console.log(val); }所以是undefined,20
var val = 12; function fun1(){ var val; console.log(val); var val = 20; console.log(val); } fun1();