JS Slider

var slides = 4;
var current = 1;
var duration = 7000; // Milliseconds
function slide(){
    document.getElementById("slide"+current).style.animation = "slide_backward 2s infinite";
    current+1;
    if(current > slides) current = 1;
    document.getElementById("slide"+current).style.animation = "slide_forward 2s infinite";
    setTimeout(slide(),duration);
}
setTimeout(slide(),duration);