Native javascript implements image carousel effect code_javascript skills

function id(name) {return document.getElementById(name);}
//Traversal function
function each(arr , callback) {
if (arr.forEach) {arr.forEach(callback);}
else {
for (var i = 0, len = arr.length; i < len; i ) callback.call(this, arr[i], i, arr);}
}
function fadeIn(elem) {
setOpacity(elem, 0)
for ( var i = 0; i < 20; i ) {
(function() {
var pos = i * 5;
setTimeout(function() {
setOpacity(elem, pos)
}, i * 25);
})(i);
}
}
function fadeOut(elem) {
for ( var i = 0; i <= 20; i ) {
(function() {
var pos = 100 - i * 5;
setTimeout(function() {
setOpacity(elem, pos)
}, i * 25);
} )(i);
}
}
// Set transparency
function setOpacity(elem, level) {
if (elem.filters) {
elem.style.filter = "alpha(opacity=" level ")";
} else {
elem.style.opacity = level / 100;
}
}