Symbols
ES6 In Depth: Symbols - Mozilla Hacks - the Web developer blog
es6 module
TIP
es6 module just a file
Modules import one another using a module loader. At runtime the module loader is responsible for locating and executing all dependencies of a module before executing it.
在node.js中经常看到使用Require node.js - The difference between "require(x)" and "import x" - Stack Overflow
