https://jscomplete.com/learn-javascript
https://jscomplete.com/javascript-higher-order-functions-callbacks
https://jscomplete.com/javascript-function-scopes-block-scopes
https://jscomplete.com/what-are-closures-in-javascript
https://jscomplete.com/javascript-function-arguments-rest-parameters
https://facebook.github.io/react/docs/dom-elements.html#style
style object & style attribute