Make a function switch what it does on every click

Question

I am trying to make a slideshow-like thing with JavaScript for a website and it isn't going well. What I want it to do is after one click change it so that it returns correctly.

Here is the code:

function previous_slide()
{
    document.getElementById('banner').className = 'banner_2';
}

I'd like to make that single function switch between its current action and this one:

document.getElementById('banner').className = 'banner_1';

so that when you press the previous button once it changes the style to banner_2 and then when you press it again it returns to banner_1.

Answer 1

previous_slide = toggle( [function(){
    document.getElementById('banner').className = 'banner_2'
}, function() {
    document.getElementById('banner').className = 'banner_1' 
}]);

Code for toggle

function toggle(functions) {
    var i = 0;
    return function() {
        return functions[i++ % functions.length].apply( this, arguments );
    }
}

Answer 2

function previous_slide()
{
  if (document.getElementById('banner').className == 'banner_2') {
      document.getElementById('banner').className = 'banner_1' 
  }
  else {
      document.getElementById('banner').className = 'banner_2'
  } 
}