Some JSDoc's improvements & comparison with 'undefined'

[AlexeyAndKartashov]

For exclude PhpStorm's warning highlight.

before:

after:

[aheckmann-pebble]

Jsdoc changes look good. Please explain why the code changes are needed.

[AlexeyAndKartashov]

Because typeof slice (second argument) may be a undefined. Comparison between number & undefined may produce different result in different js engines (perhaps). You know it =)
Just code has become a little bit a unified.