Before someone quote's crockford (http://javascript.crockford.com/code.html) I shall do it first...
> If a function literal is anonymous, there should be one space between the word function and the ( (left parenthesis). If the space is omited, then it can appear that the function's name is function, which is an incorrect reading.

Crockford's reasoning here is falls short because;
The text "function" is a reseved, so in fact a developer cannot make a function name of with function. 
It is also _easier_ to identify as an anonymous function as function() {} <i>because</i> no space and functionName is given. - IMHO (see below)
The only reason for Crockford's choice of space, is _purely_ for his own readability. For myself, I read this better without a space.

Therefore if it is purely a "is green brighter than red" question;
I would be interested into others opinions on the <b>reasoning</b> behind a space of if there is a real <i>requirement</i> for this?

Otherwise, if becomes a vote I would like to vote "no space" :)