js 预编译 函数作用域

function fn(a, c) {
        // console.log(ggggg); // Uncaught ReferenceError: ggggg is not defined
        console.log("xx : ", xx);
        console.log("yy : ", yy);
        console.log("zz : ", zz);
        var xx = function () {};
        function yy() {}
        var zz = 666;
        console.log("xx : ", xx);
        console.log("yy : ", yy);
        console.log("zz : ", zz);

        console.log("=================");

        console.log("a : ", a);
        console.log("b : ", b);
        console.log("c : ", c);
        console.log("d : ", d);
        console.log("f : ", f);
        console.log("----------------");

        a();
        // console.log("abc : ", abc); // Uncaught ReferenceError: abc is not defined
        var a = 123;
        console.log("a : ", a);
        function a() {
          console.log("function a() ...");
          console.log("abc - a() : ", abc);
          // 第一次编译期 变量不会提升 调用函数a() 创建a()的AO{}后提升
          var abc = 999;
        }
        console.log("a : ", a);
        // a(); Uncaught TypeError: a is not a function
        if (false) {
          var d = 678; // 编译期 变量也会提升
        }
        for (let index = 0; index < 10; index++) {
          var f = index; // 编译期 变量也会提升
        }
        var b = function () {};
        function c() {}
        console.log("----------------");
        console.log("a : ", a);
        console.log("b : ", b);
        console.log("c : ", c);
        console.log("d : ", d);
      }
      fn(1, 2);

xx :  undefined
yy :  ƒ yy() {}
zz :  undefined
xx :  ƒ () {}
yy :  ƒ yy() {}
zz :  666
=================
a :  ƒ a() {
    console.log("function a() ...");
    console.log("abc - a() : ", abc);
    var abc = 999;
}
b :  undefined
c :  ƒ c() {}
d :  undefined
f :  undefined
----------------
function a() ...
abc - a() :  undefined
a :  123
a :  123
----------------
a :  123
b :  ƒ () {}
c :  ƒ c() {}
d :  undefined

编译期 1.形参和变量声明赋值undefined -> 2.形参赋值 -> 3.函数声明赋值
AO{
    --------------|-----|------------------|
    a: undefined  |  1  | function a() {}  |
    c: undefined  |  2  | function c() {}  |
    b: undefined  |     |                  |
    d: undefined  |     |                  |
}