// 作用域
var a =10
function f(){
console.log('a', a)//作用域的a,var变量提升,undefined
a=100
console.log('this.a', this.a)//windows
var a
console.log('a2', a)//作用域的a,100
}
f()
var a =10
var obj ={
a:99,
f:f
}
function f(){
console.log('a', a)//作用域的a,var变量提升,undefined
a=100
console.log('this.a', this.a)//obj,99
var a
console.log('a2', a)//作用域的a,100
}
obj.f()
var a = 10
function f1() {
var b = 2 * a //2*undefined
var a = 20
var c = a + 1//20+1
console.log('b', b)//NAN
console.log('c', c)//21
}
f1()