Image Slider- Javascript

Question

Anyone have a clue why this code isn't changing my images through 1.fw.png to 5.fw.png?

HTML

<div id="slideshow">
 <img id="slider" src="1.fw.png">
</div>

JavaScript

function timer(x){
var timer = setTimeout(function () {switchPic(x);}, 4000);  
}

function switchPic(x){
x += 1;
document.getElementById('slider').src = x + ".fw.png";
}

$(document).ready()(function(){
document.getElementById('slider').src = x;
timer(x);
});

A Image Changer with a transition would be a benefit, but just changing the images is the essential requirement.

Answer 1

x is a local variable (a parameter) so the increment change does not live past the switchPic function. If there is a global x then it is shadowed; otherwise timer(x) will have resulted in a ReferenceError - make sure do describe what "isn't working" and how such is known.

I might write it like so:

jQuery(function ($) {
    var t = -1;               // initial value peicked so x is 1 at first interval
    function switchIt () {
        t++;                  // change variable caught in closure
        var x = (t % 5) + 1;  // loops through values in 1..5
        $('#slider').attr("src", x + ".fw.png");
    }
    // set initial image right away
    switchIt();
    // switch image every 4 seconds, forever
    setInterval(switchIt, 4000);
});

Answer 2

Thank you user2864740, I re-wrote the code using your information and it loops at the correct number now too.

$(document).ready(function(){
    setInterval(function(){

        z = document.getElementById('slider').src;
        y = z.indexOf(".fw.png");
        y = z.slice(y - 1, -7);
        x = parseInt(y);
        y = (x % 5) + 1;
        document.getElementById('slider').src = "/Images/Index/Slider/" + y + ".fw.png";

    },4000);
});