function f1() { number=1000;//是隐式全局变量 } f1(); console.log(number);//1000
var num1=10;
num2=20;
delete num1;//把num1删除了
delete num2;//把num2删除了
console.log(typeof num1);// number
console.log(num1+10);// 20
console.log(typeof num2);//undefined
原文：https://www.cnblogs.com/wanguofeng/p/10500091.html