javascript global variable scope

Question

So I hear that variable in js that initialized without a "var" will be global. so:

$(document).ready(function(){
      function foo(){
         //since i'm not using "var", will this function become global?
      }

      var bar = function(){
         //is this the better way to declare the function?
      }
})

If it is global, why I can't access it in the console. If it's not global, and it's scope is in the function, will omitting "var" cost some performances? Thanks.

Answer 1

Only variables declared without var become global, this does not apply to functions.

You can, however, declare foo like so:

foo = function() {}

and it should be global.

Omitting var is generally not recommended for these reasons (off the top of head):

• Variable resolution starts at the most local and goes toward looking in the global namespace, making it slower. Much slower in certain browsers.
• You tend to eventually have naming conflicts by polluting the global namespace. One of the worst offenders would be, say, for(i = 0; i < arr.length; i++) (note the lack of var)

You might want to declare functions using var due to a language feature called hoisting

BTW, if you do choose to declare functions with var, I recommend you do so this way:

var foo = function foo() {}

because it gives the function a "name" instead of being treated as an anonymous function, which will help with debugging. Most people do not do this and declare using function, I believe.