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

'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();
}
);

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

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