[JavaScript] Hoisting（巻き上げ）演習

Hoisting（巻き上げ）演習

コードの実行結果がどうなるのかを考える。

問題

[1]

var a = b = 1;

function outer() {

    console.log(a, b);

    var a = 2;

    console.log(a, b);

    function inner() {

        console.log(a, b);

        var a = 3;

        console.log(a, b);

        var b = 2;

        console.log(a, b);
    }

    inner();

    console.log(a, b);
}

console.log(a, b);

outer();

[2-1]

(function(){
    foo();

    var foo = function bar() {
        console.log(foo.name);
    };
}());

[2-2]

(function(){
    bar();

    var foo = function bar() {
        console.log(foo.name);
    };
}());

[3-1]

(function(){
    foo();

    var foo;

    foo();

    function foo() {
        console.log( 1 );
    }

    foo();

    foo = function() {
        console.log( 2 );
    };

    foo();
}());

[3-2]

(function(){
    foo();

    function foo() {
        console.log(1);
    }

    var foo = function() {
        console.log(2);
    };

    function foo() {
        console.log(3);
    }
}());

---

答え

[1]

1 1
undefined 1
2 1
undefined undefined
3 undefined
3 2
2 1

[2-1]

Uncaught TypeError: foo is not a function(…)

[2-2]

Uncaught ReferenceError: bar is not defined(…)

[3-1]

1
1
1
2

[3-2]

3