gistfile1.js

function click(theFunction) {
  // Something happens
  theFunction(event);
}

// Example 1
$('a').click(alert('hi'));

// Example 2: this does the same thing as example 1
alert_result = alert('hi');
$('a').click(alert_result);

// Example 3: this is essentially what examples 1 and 2 would be doing
alert_result(event);


/////////////////////////////////////////


// Example 4: this will work
$('a').click(function() { alert('hi') });

// Example 5: same as example 4
alert_function = function() { alert('hi') };
$('a').click(alert_function);

// Example 6: same as examples 4 and 5
alert_function(event);


/////////////////////////////////////////

// Essentially, when you call alert('hi'), you've already called the 
// function. It can't do the alert if it has been already called