Function Syntax Explanation

[n3ightjay]

Hi All I'm in need of an explanation, Im working through a sitepoint book and in one of the examples they declare a function in this syntax:

 

a.onclick = function(that){ }(this);

 

I'm having trouble understanding what the last set of parenthesis are doing ... the specific example is this:

 

a.onclick = function(that){
    return function(){
        that.sortCol(this);
        return false;
    }
}(this);

 

The book says it's so the browser handles the function immediately but is there a more detailed explanation available ... ive been hunting for a bit but haven't found anything yet