참고 문헌
- https://codeburst.io/cool-javascript-shortcuts-and-tips-for-everyday-use-66cd174ab216
- https://www.sitepoint.com/shorthand-javascript-techniques/
- https://medium.com/@kavisha.talsania/top-10-es6-features-every-javascript-developer-must-know-4c81ec54bbcd
- https://webapplog.com/es6/
- https://hackernoon.com/understanding-javascript-scope-1d4a74adcdf5