jsにおけるクロージャの説明と変数の事前宣言例（コード）

function makeFn(){
        var n1 = 100;
        function fn(){
            var n2 = 200;
            console.log(n1);
        }
        return fn;
    }
    var f2 = makeFn();
    f2();

var obj = {
        name:"sunset",
        age:12,
        speak:function(){
            console.log("我是"+this.name);
        }
    }
    console.log(obj.name);

function makeObj(){
        var name = "sunset";
        var age = 12;
        var obj = {
            speak:function(){
                console.log("我叫"+name);
            }
        }
        return obj;
    }
    console.log(obj.speak());

<script>
    for (var i = 0; i < 10; i++) {
        function makeFn(index) {
            function fn() {
                console.log(index)
            }
            return fn;
        }
        var btn = makeFn(i);
        $("<button></button>")
        .text(i + 1)
        .appendTo(document.body)
        .on("click",btn)
    }
</script>

var a = 3;
    function f1(){
       console.log(a);
       var a = 10;
    }

f1();

function f1(){
        var a;
        console.log(a);
        a = 10;
    }
f1();