Javascript 内存节省 - if 语句 var 声明

Question

如果变量驻留在不执行的 if 语句中，是否会初始化/存储在内存中，如下所示:

function blah(){
    if(something === true){
        var blahOne = 1;
        var blahTwo = 2;
        var blahThree = 3;
    } else {
        console.log('The above if statement usually won\'t execute');
    }
}

我的假设是否定的，但至少可以说 Javascript 是一种古怪的语言。预先感谢您的帮助!

Answer 1

所有 var 声明都被移动到函数的顶部并初始化为未定义。这就是所谓的变量提升。 JavaScript 没有 block 范围，只有函数和全局范围。

你的代码等同于下面的

function blah(){
    var blahOne, blahTwo, blahTree;
    if(something === true){
        blahOne = 1;
        blahTwo = 2;
        blahThree = 3;
    } else {
        // blahOne, blahTwo, blahThree are set to undefined
        console.log('The above if statement usually won\'t execute');
        // But since they have been declared, there's no error in reading them
        console.log(blahOne, blahTwo, blahThree);
    }
}