代码如下： index.js

"use strict";
console.log('a = ', a); 
try {
    console.log('b = ', b); 
}catch(e) {
    console.log(e);
}

var a  = 1;
let b = 2;

我用node index.js (node 版本为 4.4.0), 结果为:

a =  undefined
[ReferenceError: b is not defined]

但如果我用 babel-node index (babel-node 版本为 6.6.5), 结果却是:

a =  undefined
b =  undefined

.babelrc 文件配置为:

{
    "presets": [
        "es2015",
        "react"
    ],  
    "plugins": [
        "add-module-exports"
    ]   
}

为什么使用babel-node 不抛出异常呢？