javascript 函数声明问题

(function(){
    //运行正常
    test1();

    function test1() {
        console.log('123');
    };
})()

(function(){
    //出错，test2未定义

    test2();

    test2 = function () {
        console.log('123');
    };
})()

 以下摘录自《Javascript: the good parts》

/*
function statements are subject to hoisting. This means that regardless of where a
function is placed, it is moved to the top of the scope in which it is defined. This
relaxes the requirement that functions should be declared before used, which I think
leads to sloppiness. It also prohibits the use of function statements in if statements.
It turns out that most browsers allow function statements in if statements, but they
vary in how that should be interpreted. That creates portability problems.

*/