How can I make this go to a previous image instead of the next one?

Question

This is inside the head tag

<script type="text/javascript">
    var image1=new Image()
    image1.src="https://dl.dropbox.com/u/70582811/hand-eye.jpg"

    var image2=new Image()
    image2.src="https://dl.dropbox.com/u/70582811/floating.JPG"

    var image3=new Image()
    image3.src="https://dl.dropbox.com/u/70582811/lovers%20ng.jpg"
</script>

This is in the body tag

<script type="text/javascript">
    var step=1

    function slideit(){
        if (!document.images)
            return
        document.images.slide.src=eval("image"+step+".src")

        if (step<3)
            step++
        else
            step=1
        }
        slideit()
</script>

So I found this code for creating a slideshow, where I just click to step up an image. I'm calling it from a button. But I can't figure out how to alter this code so I can step back instead of forward when a different button is pressed that is a previous button. I'd appreciate any help, I'm not the best at javascript at all. Thanks in advance.

This is where I'm at: http://slidetester.tumblr.com/

Answer 1

You will need to make it so rather than incrementing the picture via step++ the picture number is decremented. Look up how to do this. Also you will need to change the condition for when it runs out of pictures to go back to. I don't want to give you the full code as this should be a learning experience.

Answer 2

I'm assuming you know how to make a button and assign a separate function to it, so instead of slideit() we can call another function which we can call slideitbackwards()

function slideitbackwards() {
  if (!document.images)
    return
  document.images.slide.src=eval("image"+step+".src")
  if (step > 1) //Change this line to the minimum image number
    step-- //subtract instead of add
  else
    step = 3 //Set this to maximum value instead of minimum
  }

Answer 3

创建一个新函数并通过按钮触发它：function slideitBack（）{if（！document.images）返回document.images.slide.src = eval（“ image” + step +“。src”）if（step> 1 ）step-- else step = 3}