<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>