JavaScript to achieve fireworks effects (object-oriented)

class FireWork{
    constructor(){
        
    }
    bindEvent(){
        let _this = this;
        ele.onclick = function(){
            //After fly is finished, call the boom function_this.fly(_this.boom);
        }
    }
    fly(boom){
        
    }
    boom(){
        
    }
}

 *{
        margin: 0;
        padding: 0;
    }
    #box{
        width:800px;
        height:600px;
        position: relative;
        margin: 100px auto;
        background:#000000;
        border:2px solid red;
        overflow: hidden;
    }
    .ball{
        width: 40px;
        height: 40px;
        border-radius: 50%;
        position: absolute;
        bottom: 0;
    }

<script src="./utils.js"></script>
<script>
// 
class FireWork{
    constructor(){
        this.box = document.getElementById("box");
        this.box_offset = {
              left : box.offsetLeft,
              top : box.offsetTop
        }
    }
    bindEvent(){
        let _this = this;
        this.box.onclick = function( e ){
              e = e || event;
              _this.x = e.clientX - _this.box_offset.left; 
              _this.y = e.clientY - _this.box_offset.top; 
    
              _this.fly(_this.boom);
        }     
    }     
    fly(boom ){
        let ele = this.createEle();
        let _this = this;
        //Put it in the box; 
        ele.style.left = this.x + "px";
    
        let _left = this.x ; 
        let _top = this.y ; 
    
        animate(ele, {
              top : this.y 
        } , function(){
              ele.remove();
              _this.boom( _left , _top );
        });
    }
    boom( x , y ){
        let r = 100;
        let count = 0 ; 
        let _this = this;
    
        for(let i = 0 ; i < 20 ; i ++){
              let ele = this.createEle();
              ele.style.left = x + "px";
              ele.style.top = y + "px";
              let _left = parseInt(Math.cos( Math.PI / 10 * i ) * r ) + x ;
              let _top = parseInt(Math.sin( Math.PI / 10 * i ) * r) + y
              animate(ele, {
                    left : _left,
                    top : _top,
                    opacity : 0 
              } , function(){
                    ele.remove();
              })
        }
    }
    createEle(){
        let ele = document.createElement("div");
        ele.className = "ball";
        ele.style.backgroundColor = `rgb(${parseInt(Math.random() * 255)},${parseInt(Math.random() * 255)},${parseInt(Math.random() * 255)})`;
        this.box.appendChild(ele);
        return ele ; 
    }
}

new FireWork().bindEvent();
</script>

function on(dom, event_name, handler_selector, delegation_handler) {
    if( typeof handler_selector === "string" && typeof delegation_handler === "function"){
        return delegation(dom, event_name, handler_selector, delegation_handler);
    }
    // Create an event name in the DOM object: an array corresponding to the event processing function; 
    // Determine whether the current event processing function is in the DOM object;
    var event_type = "_" + event_name;
    if (event_type in dom) {
        dom[event_type].push(handler_selector);
    } else {
        dom[event_type] = [handler_selector];
    }
    // If you use the event name directly as the key value in the object, it will conflict with the original DOM function name; 
    // Because special event names will cause the event to fail to trigger, we need to split the event name here; 
    dom.addEventListener(event_name.split(".")[0], handler_selector)
}
function off(dom, event_name) {
    // Get a set of event processing functions corresponding to the event name in the DOM object; 
    var callback_list = dom["_" + event_name];
    // Remove events according to all functions in the list; 
    callback_list.forEach(function (event_handler) {
        dom.removeEventListener(event_name.split(".")[0], event_handler);
    })
    // Clear the event processing function group in the DOM object; 
    dom["_" + event_name].length = 0;
}
    
function trigger(dom, event_type) {
    dom.dispatchEvent(new Event(event_type));
}
    
function delegation(dom, event_name, selector, event_handler) {
    dom.addEventListener(event_name, function (e) {
        e = e || event;
        var target = e.target || e.srcElement;
        while (target !== dom) {
              switch (selector[0]) {
                    case ".":
                          if (selector.slice(1) === target.className) {
                                event_handler.call(target , e )
                                return;
                          }
                    case "#":
                          if (selector.slice(1) === target.id) {
                                event_handler.call(target, e)
                                return;
                          }
                    default:
                          if (selector.toUpperCase() === target.nodeName) {
                                event_handler.call(target, e)
                                return;
                          }
              }
              target = target.parentNode;
        }
    })
}


function animate( dom , attrs , callback , transition = "buffer", speed = 10 ){
    // transition: There are two animation modes: "buffer" and "liner"
    var _style = getComputedStyle( dom );
    
    // - 1. Data deformation; 
    for(var attr in attrs ){
        attrs[attr] = {
              target : attrs[attr],
              now : _style[attr]
        }
        // - 2. Speed: positive or negative speed of uniform motion; 
        if( transition === "liner" ){
              attrs[attr].speed = attrs[attr].target > attrs[attr].now ? speed : - speed;
        }
    
        if( attr === "opacity"){
              attrs[attr].target *= 100 
              attrs[attr].now *= 100
        }else{
              attrs[attr].now = parseInt(attrs[attr].now) 
        }
    }
    // - turn off the start timer;    
    clearInterval( dom.interval );
    dom.interval = setInterval( function() {
        for(var attr in attrs ){
              // Get the current value and attribute value; 
              // attrs[attr].target : target value; 
              // attrs[attr].now : current value; 
    
              let { target , now } = attrs[attr];
    
              // Buffering speed; 
              if( transition === "buffer" ){
                    var speed = (target - now ) / 10 ;
                    speed = speed > 0 ? Math.ceil( speed ) : Math.floor( speed );
              }else if(transition === "liner"){
                    var speed = attrs[attr].speed; 
              }
    
              
              if( Math.abs(target - now) <= Math.abs( speed ) ){
                    
                    if( attr === "opacity"){
                          dom.style[attr] = target / 100;
                    }else{
                          dom.style[attr] = target + "px";
                    }
    
                    delete attrs[attr];
                    for(var attr in attrs ){
                          // If there is data, the loop will be executed at least once; 
                          return false;
                    }
                    clearInterval(dom.interval);
                    typeof callback === "function" ? callback() : "";
              }else{
                    now += speed;
    
                    if( attr === "opacity"){
                          dom.style[attr] = now / 100;
                    }else{
                          dom.style[attr] = now + "px";
                    }
                    // Assign a value to the object; 
                    attrs[attr].now = now;
              }
        }
    } , 30)
}