最近写了一个红包雨的小功能，但感觉自己的js还有很多地方可以提高，望大神们可以帮忙指点一二

js部分

'use strict';
function RedEnvelope(options){
    if(this === window){
        return new RedEnvelope(options);
    }
    var defaults = {
        imgWidth:60,//红包的宽度
        position:'absolute',
        imgEnvSrc:'../images/game/redEnv/redEnv.png',
        containerClass:'.redEnv-contain'
    };
    if(!options){
        options = defaults;
    }else{
        for (var option in defaults) {
            if (typeof options[option] === undefined) {
                options[option] = defaults[option];
            }
        }
    }
    this.options = options;
    this.createEnv();
}
RedEnvelope.prototype.createEnv = function(){
    var imgEnv = document.createElement('img');
    imgEnv.src = this.options.imgEnvSrc;
    imgEnv.style.width = this.options.imgWidth+'px';
    this.evnPosition(imgEnv);
}
RedEnvelope.prototype.evnPosition = function(img){
    var containerWidth = $(this.options.containerClass).width();
    var containerHeight = window.screen.height;
    $(this.options.containerClass).prepend(img);
    //红包初始的位置
    img.style.position = this.options.position;
    var startTop = parseInt(Math.random()*10+(-10))
    var startLeft = parseInt(Math.random()*containerWidth);
    //移动的位置
    var moveLeft = parseInt(Math.random()*containerWidth+(-30));
    var t=parseInt(Math.random() * 1000+1200);
    this.evnAnimation({'startLeft':startLeft, 'startTop':startTop, 'moveLeft':moveLeft,'moveTop':containerHeight},t);
}
/*添加元素到主内容上*/
RedEnvelope.prototype.evnAnimation =  function (posObject,time){
    $(this.options.containerClass).children('img:first').css({'left':posObject.startLeft,'top':posObject.startTop});
    $(this.options.containerClass).children('img:first').animate(
        {
            'left':posObject.startLeft-posObject.moveLeft,
            'top':posObject.moveTop
        },
        time,
        'linear',
        function(){
            $(this).remove();
        }
    );
    

html部分

<div class="redEnv-contain">
</div>

<script>
	setInterval(RedEnvelope,500);	
</script>