Whats the porpuse of i = 1; on this function?

var image = ['a','b', 'c', 'd','e'];

var i = image.length;

function nextImage(){
    	if (i<image.length) {
    		i= i+1;
    		i = 1;
    	  slider_content.innerHTML = "<img src="+image[i-1]+".jpg>";

Because the else block of code means that i is greater or equal to the length of the array. This means the end of the array has been reached, so setting i=1 resets the slideshow back to the first image as image[i-1] refers to the element at index 0 (the first element).