js彈幕

var danmu = {
                        play_width : 0, //銀幕寬
                        play_height : 0, //銀幕高
                        msg_stu : {}, //彈幕結構
                        msg_queue : [], //彈幕隊列
                        play_screen : null,
                        addmsg : function(text){
                            mathHeight = Math.round(Math.random()*this.play_height);
                            speed = Math.round(5+Math.random()*20);
                            var msg = {
                                'left' : this.play_width,
                                'top' : mathHeight,
                                'text' : text,
                                'speed' : speed,
                            };
                            this.msg_queue.push(msg);
                        },
                        play : function(){
                            var i = 0;
                            for(var msg in this.msg_queue){
                                console.log(i);
                                if(this.msg_queue[i].left<(0-this.play_width)){
                                    this.removemsg(i);
                                }else{
                                    this.playmsg(i);
                                }
                                i++;
                            }
                        },
                        playmsg : function(i){
                            bullet = document.getElementById('zidan_'+i);
                            if(bullet!=undefined){
                                //子彈飛
                                this.msg_queue[i].left -= this.msg_queue[i].speed;
                                bullet.style.left = this.msg_queue[i].left+'px';
                                bullet.style.top = this.msg_queue[i].top+'px';
                            }else{
                                //建立子彈
                                b = document.createElement("font");
                                b.id = 'zidan_'+i;
                                msg = this.msg_queue[i];
                                b.style.position = 'absolute';
                                b.style.color = '#fff';
                                b.style.left = msg.left+'px';
                                b.style.top = msg.top+'px';
                                b.innerHTML = msg.text;
                                this.play_screen.appendChild(b);
                            }
                        },
                        removemsg : function(i){
                            bullet = document.getElementById('zidan_'+i);
                            bullet.style.left = this.play_width+'px';
                            this.msg_queue[i].left = this.play_width;
                        },
                        init : function(playid,btnid,textid){
                            this.play_width = document.getElementById(playid).offsetWidth;
                            this.play_height = document.getElementById(playid).offsetHeight;
                            this.play_screen = document.getElementById(playid);
                            this.play_screen.style.position = 'relative';
                            document.getElementById(btnid).onclick = function(){
                                danmu.addmsg(document.getElementById(textid).value);
                                console.log(danmu.msg_queue);
                            };
                            setInterval(function(){
                                danmu.play();
                            },50);
                        }
                    };
                    danmu.init('tangmu','inputBtn','inputText');

<div class="danmuBox"><div id="tangmu">2</div></div>
                     <div class="form">
                        <form>
                            <input type="text" placeholder="愛要大聲說出來..." value="" maxlength="30" id="inputText" class="textarea" id="text">
                            <input type="button" value="向世界發佈" class="submit inputBtn" id="inputBtn">
                            <input type="reset" value="不發了- -#" name="reset" class="reset inputBtn">
                        </form>
                    </div>