js,模拟弹幕发射，有些bug不明白，求帮助、、、

Question

var subtitle = document.getElementById("subtitle");
var fire = document.getElementById("fire");
var colordict = {"bl":"#666666","r":"#ff00ff","g":"#66ff33","b":"#6633ff"}
var subtitlelist = new Array();
var subword = new Object();
var timercreated = false;
function update(t){
    var subwo = document.getElementsByClassName("subword");
    if (subtitlelist.length<=0 && timercreated==true)
    {
        clearInterval(t);
        timercreated = false;
    }else{
        for (var i=0;i<subtitlelist.length;i++)
        {
            if (subtitlelist[i]["left"] < -parseInt(subwo[i].clientWidth))
            {
                subtitlelist.splice(i,1);
                page1.removeChild(subwo[i]);
            }else{
                subtitlelist[i]["left"]-=3;
                console.log(subtitlelist[i]["left"]);
                subwo[i].style.left = subtitlelist[i]["left"]+"px";
            }
        }
    }
}
fire.onclick = function(){
    if (timercreated==false)
    {
        console.log(timercreated);
        window.t = setInterval(update,500);
        timercreated = true;
    }

    var colorvalue = document.getElementsByName("color");
    if (subtitle.value==null||subtitle.value=="")
    {
        return;
    }else{
        if (subtitlelist.length<=50)
        {
            subword["word"] = subtitle.value;
            for (var i=0;i<colorvalue.length;i++)
            {
                if (colorvalue[i].checked==true)
                {
                    subword["color"] = colordict[colorvalue[i].value];
                    break;
                }
            }
            subword["left"] = 792;
            subword["top"] = parseInt(Math.random()*600)+"px";
            subword["iscread"] = false;

            subw = document.createElement("span");
            subw.className = "subword";
            subw.style.color = subword["color"];
            subw.innerText = subword["word"];
            subw.style.left = subword["left"]+"px";
            subw.style.top = subword["top"];
            page1.appendChild(subw);
            subword["iscread"] = true;
            subtitlelist.push(subword);
        }else{
            alert("弹幕是有上限的，请待会在发");
        }

    }

}
![图片说明](https://img-ask.csdn.net/upload/201808/03/1533302489_63655.png)

问题  1、同时发射多个弹幕（2个以上），前面的弹幕“left”会重置，回到屏幕右侧。
       2、发射多个时，弹幕的速度好像会叠加。

Answer 1

 var subtitle = document.getElementById("subtitle");
var fire = document.getElementById("fire");
var colordict = {"bl":"#666666","r":"#ff00ff","g":"#66ff33","b":"#6633ff"}
var subtitlelist = new Array();
//var subword = new Object();
var timercreated = false;
function update(){//------------不要写t参数
    var subwo = document.getElementsByClassName("subword");
    if (subtitlelist.length<=0 && timercreated==true)
    {
        clearInterval(t);
        timercreated = false;
    }else{
        for (var i=0;i<subtitlelist.length;i++)
        {
            if (subtitlelist[i]["left"] < -parseInt(subwo[i].clientWidth))
            {
                subtitlelist.splice(i,1);
                page1.removeChild(subwo[i]);
            }else{
                subtitlelist[i]["left"]-=3;
                console.log(subtitlelist[i]["left"]);
                subwo[i].style.left = subtitlelist[i]["left"]+"px";
            }
        }
    }
}
fire.onclick = function(){
    if (timercreated==false)
    {
        console.log(timercreated);
        window.t = setInterval(update,500);
        timercreated = true;
    }

    var colorvalue = document.getElementsByName("color");
    if (subtitle.value==null||subtitle.value=="")
    {
        return;
    }else{
        if (subtitlelist.length<=50)
        {
            var subword = new Object();//------每次都要创建新的对象
            subword["word"] = subtitle.value;
            for (var i=0;i<colorvalue.length;i++)
            {
                if (colorvalue[i].checked==true)
                {
                    subword["color"] = colordict[colorvalue[i].value];
                    break;
                }
            }
            subword["left"] = 792;
            subword["top"] = parseInt(Math.random()*600)+"px";
            subword["iscread"] = false;

            subw = document.createElement("span");
            subw.className = "subword";
            subw.style.color = subword["color"];
            subw.innerText = subword["word"];
            subw.style.left = subword["left"]+"px";
            subw.style.top = subword["top"];
            page1.appendChild(subw);
            subword["iscread"] = true;
            subtitlelist.push(subword);
        }else{
            alert("弹幕是有上限的，请待会在发");
        }

    }

}