Resolve issues with JSLint

See http://www.jslint.com.

- Add missing semicolons
- Wrap `if` statement with braces
- Use `!==` and `===` instead of `!=` and `==`
- Use hexadecimal escapes instead of octal escapes
    - Octal escapes have been deprecated in ES5 and they produce syntax errors in strict mode. See https://mathiasbynens.be/notes/javascript-escapes#octal.