Check if your page is visible currently via javascript

Link here.

Learn how to use flexbox to position elements

Link here.

Extract and manipulate rar files using javascript !

Link here.

Really cool concept of automatically switching to lighter or darker version of an element depending on the brightness of images behind it.

Link here.

A quick 3 minutes introduction to Bower( Javascript Package Manager)

Link here.

A nice and minimalistic progress bar

Link here.

Coolest ever page transitions !

Link here.

Preload assets(eg. images) on your page

Link here.

Know which css is going unused

Link here.

Tired of figuring out how to vertically(or horizontally) center your elements? Here's a javascript plugin!

Link here.

Get placeholder images according to your need when designing a new web app

I could find not one but three of them. Besides choosing sizes, we can also choose type of images we want from categories provided, all for free.

Lorem Pixel
Fakeimg
Placeimg

Easy library to make charts and graphs

Link here.

Want to minimize your minimized files more through structural optimization?

Link here.

A command line tool to generate css sprites.

Link here.

Sencha gives you a free way to resize your big images on smaller screens.

Link here.

Count character, words and paragraphs entered by a user live

A very small plugin that has no dependencies.
Link here.

A plugin if you want to use excel/spreadsheet formulas.

Link here.

Ready css3 animations

Link here.

Know the resolution and ppi of any screen

Link here.

Write better html using HTML inspector plugin

Link here.