((speed < 0 && parseInt(list.style.left) > newLeft) || (speed > 0 && parseInt(list.style.left) < newLeft))这是什么意思

window.onload = function(){

var container = document.getElementById('container');

var list = document.getElementById('list');

var buttons = document.getElementById('buttons').getElementsByTagName('span');

var prev = document.getElementById('prev');

var next = document.getElementById('next');

var index = 1;

function showButton(){

for (var i = 0; i < buttons.length; i++) {

if(buttons[i].className == 'on'){

buttons[i].className = '';

break;

}

}

buttons[index - 1].className = 'on';

}

function animate(offset){

var newLeft =  parseInt(list.style.left) + offset;

var time = 300;

var interval = 10;

var speed = offset/(time/interval);

function go(){

if((speed < 0 && parseInt(list.style.left) > newLeft) || (speed > 0 && parseInt(list.style.left) < newLeft)){

list.style.left = parseInt(list.style.left) + speed + 'px';

setTimeout(go, interval);

}else {

list.style.left = newLeft + 'px';

if (newLeft < -3000) {

list.style.left = -600 +'px';

}else if(newLeft > -600){

list.style.left = -3000 +'px';

}

}

}

go();

}

next.onclick = function(){

if(index == 5){

index = 1;

}else {

index += 1;

}

showButton();

animate(-600);

}

prev.onclick = function(){

if(index == 1){

index = 5;

}else {

index -= 1;

}

showButton();

animate(600);

}

for(var i = 0; i < buttons.length ; i++){

buttons[i].onclick = function(){

if(this.className == 'on'){

return;

}

var myIndex = parseInt(this.getAttribute('index'));

var offset = -600 * (myIndex - index);

animate(offset);

index = myIndex;

showButton();

}

}