html - JavaScript Hoisting declaration confusion when using Immediately-invoked function expression -

get confused.

var message = "xinrui ma";  var call = (function(){     message = "i cool"; })();  alert(message); 

from perspective, code treated this:

var message = "xinrui ma";  var call = (function(){     var message;         // add message declaration here     message = "i cool"; })();  alert(message);        // should alert "xinrui ma", not "i cool",                         // cause hoisting javascript's default behavior of moving declarations                         // top of current scope  

but in fact, outputs "i cool", why that????

if don't have variable declaration inside function, uses variable containing scope. doesn't create new local variable -- there wouldn't way refer closure variables if did that.

this has nothing hoisting, occurs when declare variable in function. hoisting apply if wrote:

var call = (function() {     message = "i cool";     var message; })(); 

in case, var declaration hoisted top of function.