将属性和方法添加到Date原型中

<button onclick="myFunction()">点我</button>
<script>
Date.prototype.myMet=function(){
    if (this.getMonth()==0){this.myProp="一月"};
    if (this.getMonth()==1){this.myProp="二月"};
    if (this.getMonth()==2){this.myProp="三月"};
    if (this.getMonth()==3){this.myProp="四月"};
    if (this.getMonth()==4){this.myProp="五月"};
    if (this.getMonth()==5){this.myProp="六月"};
    if (this.getMonth()==6){this.myProp="七月"};
    if (this.getMonth()==7){this.myProp="八月"};
    if (this.getMonth()==8){this.myProp="九月"};
    if (this.getMonth()==9){this.myProp="十月"};
    if (this.getMonth()==10){this.myProp="十一月"};
    if (this.getMonth()==11){this.myProp="十二月"};
}
function myFunction(){
    var d = new Date();
    d.myMet();
    var x=document.getElementById("demo");
    x.innerHTML=d.myProp;
}
</script>