1.函数声明整体提升
2.变量 声明提升
3.一切声明的全局变量，全是window的属性

预编译过程：
1.创建AO对象
2.找形参和变量声明，将变量和形参作为AO属性名，值为undefined
3.将实参值和形参值统一
4.在函数体里面找函数声明，值赋予函数体

1

function fn(a){
    console.log(a);//function a(){}
    var a=123;
    console.log(a);//123
    function a(){}
    console.log(a)//123
    var b = function(){}
    console.log(b);//function(){}
    function d(){}
}
fn(1)

2

function test(a,b){
    console.log(a); //1
    c=0;
    var c;
    a=3;
    b=2;
    console.log(b)//2
    function b(){}
    function d(){}
    console.log(b)//2
    
}
    
test(1)

3

function test(a,b){
    console.log(a);//ƒ a(){}
    console.log(b);//undefined
    var b=234;
    console.log(b);//234
    a=123;
    console.log(a);//123
    function a(){}
    var a;
    b=234;
    var b=function(){}
    console.log(a);//123
    console.log(b);//ƒ (){}
}

test(1)

4

console.log(test) //function test(test){
function test(test){
    console.log(test) //function test(){}
    var test = 234;
    console.log(test)//234
    function test(){}
}
test(1);
var test = 123

5

var global = 100;

function fn(){
    console.log(global) //100
}
fn()

globel = 100;
function fn(){
    console.log(globel)//undefiend
    globel = 200;
    console.log(globel)//200
    var globel = 300;
}
fn();
var global;

6

function test(){
    console.log(b)//undefiend
    if(a){
        var b=100;
    }
    console.log(b)//undefiend
    c=234;
    console.log(c)//234
}

var a;
test();
a=10;
console.log(c)//234

7

function bar(){
    return foo;
    foo = 10;
    function foo(){}
    var foo = 11;
}
            
console.log(bar())      //function foo(){}  

8

  var b = "boy";
   console.log(b); // boy
   function fighting(){
    
    console.log(a); //undefiend
    console.log(c);  //undefiend
    if(a === "apple"){
     a = "Alice"
    }else{
     a = "Ada"
    }
    console.log(a)  //Ada
    var a = "Andy"; 
    middle();
    function middle(){
     console.log(c++); //NaN
     var c = 100;
     console.log(++c); //101
     small();
     function small(){
      console.log(a)  //Andy
     }
    }
    var c = a = 88;
    function bottom(){
     
     console.log(this.b); //boy
     b = "baby";
     console.log(b) //baby
    }
    bottom();
    
   }
   fighting();
   console.log(b)//baby