24.作用域

// 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()