临时死区（ES6）似乎不起作用

Question

Below is my code: 下面是我的代码：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

</head>
<body>
<h1 id="message"></h1>

<script src="traceur/traceur.js"></script>
<script src="traceur/BrowserSystem.js"></script>
<script src="traceur/bootstrap.js"></script>
<script type="module">

    var x = 'outer scope';
    (function() {
        console.log(x); //Expected undefined, got undefined ! this is as expected.
        var x = 'inner scope';
    }());

    //same as above, but changed to var to let and x to y
    let y = 'outer scope';
    (function() {
        console.log(y); //Was expecting ReferenceError here, but got undefined. WTF ??!!!
        let y = 'inner scope';
    }());


</script>

</body>
</html>

Its seems the temporal drop zone (TDZ) in es6 should throw a referenceError in case the let-var is used before it is declared. 似乎在es6中的临时拖放区（TDZ）应该抛出referenceError，以防在声明之前使用let-var。

However, in this example, I am getting undefined for let. 但是，在此示例中，我对let的定义变得不确定。 Where am i going wrong? 我要去哪里错了？

Been at this problem for a long time and wasted a day on this. 很久以来一直在解决这个问题，并为此浪费了一天。 (Any pointers would be very help). （任何指针都将非常有帮助）。 I am using Chrome v58. 我正在使用Chrome v58。

v58 has es6 compatibility as per https://kangax.github.io/compat-table/es6/ under current browser). 根据目前浏览器的https://kangax.github.io/compat-table/es6/，v58具有es6兼容性）。

I stripped off the traceur part and posted on babel-try it out, and got the same result. 我剥去了示踪剂部分，并贴上了通心粉试一下，得到了相同的结果。

Am wondering why is it not working in my chrome v58. 我想知道为什么我的Chrome v58无法正常工作。 Maybe it requires something else too?? 也许还需要其他东西吗？

Answer 1

You are using Traceur, which does not support TDZ for let/const . 您正在使用Traceur，它不支持TDZ的let / const 。 It will convert let to var - making the TDZ behaviour for let identical to your var example. 它会转换let到var -制作用于让相同的变种例如TDZ行为。 Run the same code in an ES6-compatible environment and you'll see the expected result: 在与ES6兼容的环境中运行相同的代码，您将看到预期的结果：

 var x = 'outer scope'; (function() { console.log(x); var x = 'inner scope'; }()); let y = 'outer scope'; (function() { console.log(y); let y = 'inner scope'; }());

Answer 2

I removed the transpiler code and enabled the Experimental Features in JS chrome://flags/#enable-javascript-harmony here and it worked as expected now. 我删除了转译器代码，并在JS chrome：// flags /＃enable-javascript-harmony中启用了实验性功能，现在可以正常使用了。

Chrome version v58 Chrome版本v58

临时死区（ES6）似乎不起作用

问题描述

2 个解决方案

解决方案1
0 2017-06-05 08:09:30

解决方案2
0 2017-06-05 09:00:51

临时死区（ES6）似乎不起作用

问题描述

2 个解决方案

解决方案1 0 2017-06-05 08:09:30

解决方案2 0 2017-06-05 09:00:51

解决方案1
0 2017-06-05 08:09:30

解决方案2
0 2017-06-05 09:00:51