JavaScript variable declaration elevation (hoisting)

When I first started using JS, I felt that the language was so simple. Very fast to use. But when I ask myself, the essence of JS, where the characteristics, just don't need to define the type,

You don't need to manage your own memory. The initial understanding of JS is limited to this.

Always understand is that JS is an explanatory language, the code line parsing down, suddenly found a way, let me have doubts about this, after Baidu finally

Know why. Here I briefly record the next.

Count (on); function count (b) {    + b);  }

The result is normal.

var test = "AAA"; function func () {  console.log (test);   var test = "BBB";    }

The result is undifined.

JS variable declares the beauty of the promotion mechanism. This article is well written.

Http://openwares.net/js/javascript_declaration_hoisting.html

JavaScript variable declaration elevation (hoisting)