jQuery pls wait

plswait.js

$.fn.plswait = function(command, arg1){
     this.each(function(){
         function loadingBtnOverlay(el) {
             this.element = $(el);
             this.overlay = null;
             return this;
             }
                    
                    loadingBtnOverlay.prototype.start = function (btn){
                    if(!$('body > #sclupndown-anim').is('*')){
                        $('body').append('<style id="sclupndown-anim"> @keyframes sclupndown{ 25%{ transform: scale(1); box-shadow: 1px 1px 2px 0px rgba(0,0,0,0.1) } 50%{ transform: scale(1.5); box-shadow: 3px 3px 5px 0px rgba(0,0,0,0.1) } 100%{ transform: scale(1); box-shadow: 1px 1px 2px 0px rgba(0,0,0,0.1) }}</style>');
                    }
                    var _this = this;
                    this.stop().then(function(){        
                        _this.overlay = $('<div class="loading-btn-overlay">')

                        for(var i=0; i<5; i++){
                            var $dot = $('<div class="loading-dot"> </div>');
                            $dot.css({
                                 width: 10,
                                 height: 10,
                                 backgroundColor: '#fff',
                                 borderRadius: '50%',
                                 margin: '0 2%',
                                 animation: 'sclupndown .7s',
                                 animationIterationCount: 'infinite',
                                 boxShadow: '1px 1px 2px 0px rgba(0,0,0,0.1)'
                            });
                            $dot.css('animation-delay', .1*i +'s');
                            _this.overlay.append($dot);
                        }

                        _this.overlay.css({
                            display: 'flex',
                            justifyContent: 'center',
                            alignItems: 'center',
                            position: 'absolute',
                            top: _this.element.position().top,
                            left: _this.element.position().left,
                            backgroundColor: '#7796a8',
                            width: _this.element.outerWidth(),
                            height: _this.element.outerHeight(),
                            opacity: 0,
                            transition: 'opacity .3s',
                            zIndex: 100
                        });

                        _this.element.offsetParent().append(_this.overlay)
                        var overlay = _this.overlay;
                        setTimeout(function(){
                            overlay.css('opacity', 1);
                        }, 50);
                    });
                    }
              loadingBtnOverlay.prototype.stop = function(){
                   var _this = this;
                   return new Promise(function(res){
                        var overlay = _this.overlay;
                        if(overlay){
                            overlay.css('opacity', 0);
                        setTimeout(function(){
                            overlay.remove();
                            res();
                            }, 300);   
                        }else{
                            res();
                        }
                        });
                    }
           this.loading = this.loading || new loadingBtnOverlay(this);
           
           switch(command){
            case 'stop':
                this.loading.stop()
            break;
            case 'start':
                this.loading.start()
            break;
            default:
                this.loading.start()
            break;
        }
    });
    return this;
}

// example usage
// $(selector).plswait();
// $(selector).plswait('stop');