(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 afunction is placed, it is moved to the top of the scope in which it is defined. Thisrelaxes the requirement that functions should be declared before used, which I thinkleads 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 theyvary in how that should be interpreted. That creates portability problems.*/