JavaScript Hoisting

Hoisting is JavaScript's default behavior of moving all declarations to the top of the current scope (to the top of the current script or the current function).

function number() {
    return 1;
}

(function() {
    try {
        number();
    } catch (ex) {
        console.log(ex);
    }
    var number = function number() {
        return 2;
    };

    console.log(number());
})();

console.log(number());

js會把宣告提升到當前作用域的最上邊，包括變數和函式宣告。

function number() {
    return 1;
}

(function() {
    console.log(number());

    function number() {
        return 2;
    }
})();

console.log(number());