자바스크립트에서 strict mode를 사용해야 하는 이유

Problem at line 1 character 1: Missing "use strict" statement.

Ref

• http://stackoverflow.com/questions/1335851/what-does-use-strict-do-in-javascript-and-what-is-the-reasoning-behind-it
• http://blog.aliencube.org/ko/2014/01/02/reasons-behind-using-strict-mode-while-coding-javascript/