js高级-函数变量提升
var a = 10;
function f1(){
console.log(a) //undefined 函数变量提升了 函数执行之前想创建了函数的EC 把函数里面声明的变量初始化undefined a先访问了f1内部的了
var a = 19; 给局部变量赋值
console.log(a) 19
}
f1();
// 面试题
1、
var a = 18;
function d(){
console.log(a) //undefined 内部变量a提升
var a = {age:19}
console.log(a) // {age:19}
}
d();
console.log(a) //18
2、
if(!("a" in window)){ //"a" in window true 因为 var a =9 变量提升了
var a = 1;
}
console.log(a) //undefined
3、
console.log(a) //function a(){}
var a = 20;
console.log(a) //20
function a(){
}
4、
f()
console.log(a) // 报错未定义
console.log(b) //9
console.log(c) //9
function f(){
var a = b = c = 9; a局部变量 bc全局变量 var a= 9,b=9,c=9;定义三个局部变量
console.log(a) //9
console.log(b) //9
console.log(c) //9
}
5、
f()
function f(){
for(var k=0; k<10; k++){
console.log(k) //0-9
}
console.log(k) //10
}