几个求值js

var a = 1;
    function aa(){
        a = 2;
    }
    aa();
    console.log("a:", a);         // 2

    var b = 1;
    function bb(){
        b = 2;
        var b = 3;
    }
    bb();
    console.log("b:", b);        // 1

    function foo(){
        var a1 = 1;
        function fn1(){
            fn2();
            var a1 = 3;
        }
        function fn2(){
            a1 = 2;
        }
        fn1();
        return a1;
    }
    var c = foo();
    console.log("c:", c)        // 2

    function foo2(){
        var a2 = 1;
        function fn1(){
            a2 = 2;
            var a2 = 3;
        }
        
        fn1();
        return a2;
    }
    var d = foo2();
    console.log("d:", d)        // 1

注意函数的闭包作用域，变量声明提前，变量不加var 时候是全局变量，及函数执行环境