javascript - 为什么 nextButton() 函数没有运行？

Question

我还是个新手，正在尝试制作一个简单的网站，我的功能之一是日历。

为什么我的函数 nextbutton() 没有运行？

我还需要一些批评家，我应该在编码中更改哪些地方以及哪些内容。非常感谢!

    function calendar(){    
        date = new Date();
        month = date.getMonth();
        year = date.getFullYear();
        var dayOfweek = date.getDay();      
        var day = date.getDate();
        var nameOftheMonth = ["JANUARY", "FEBRUARY", "MARCH", "APRIL", "MAY", "JUNE", "JULY", "AUGUST", "SEPTEMBER", "OCTOBER", "NOVEMBER", "DECEMBER"];
        var nameOftheDays = ["SUN", "MON", "TUE", "WED", "THU", "FRI", "SAT"];
        var nextMonth = month+1;
        var prevMonth = month-1;
        var numberOfDays = new Date(year, month, 1).getDay();
        var TotalNumOfDays = new Date(year, month+1, 0).getDate();
        var num2 = numberOfDays+1;
        var num = 1;
        var content = "";

        content += "<button><----</button><div>" + nameOftheMonth[month] + " " + year + "</div><button>----></button>"; 

        content += "<br/><table><tr>";                  
        for (count=0;count <= nameOftheDays.length-1; count++){

            content += "<td>" + nameOftheDays[count] + "</td>"; 

            if(count === nameOftheDays.length-1){
                content += "</tr><tr>";
            }
        }           
        while (numberOfDays > 0) {  
                content += "<td></td>";
                numberOfDays--;
        }

        while (num <= TotalNumOfDays){
            content += "<td>" + num + "</td>";
            if (num2 > 6) {
                num2 = 0;
                content += "</tr><tr>"
            }
            num2++;
            num++;              
        }   

        document.getElementById("calendar").innerHTML = content;
        document.getElementsByTagName("button")[0].setAttribute("id", "prevbutton");
        document.getElementsByTagName("button")[0].setAttribute("onclick", "prevButton()");     
        document.getElementsByTagName("button")[1].setAttribute("id", "nextButton");
        document.getElementsByTagName("button")[1].setAttribute("onclick", "nextButton()");
        document.getElementsByTagName("div")[1].setAttribute("id", "dateToday");

    }
    function nextButton(){
        if(month != null){
            month = month++;
        }
    }

Answer 1

<div id="calendar"></div>

<script language="JavaScript">      
var month=-1;
 function calendar(){  
        date = new Date();
        if(month===-1){
        month =date.getMonth();
        }
        year = date.getFullYear();
        var dayOfweek = date.getDay();      
        var day = date.getDate();
        var nameOftheMonth = ["JANUARY", "FEBRUARY", "MARCH", "APRIL", "MAY", "JUNE", "JULY", "AUGUST", "SEPTEMBER", "OCTOBER", "NOVEMBER", "DECEMBER"];
        var nameOftheDays = ["SUN", "MON", "TUE", "WED", "THU", "FRI", "SAT"];
        var nextMonth = month+1;
        var prevMonth = month-1;
        var numberOfDays = new Date(year, month, 1).getDay();
        var TotalNumOfDays = new Date(year, month+1, 0).getDate();
        var num2 = numberOfDays+1;
        var num = 1;
        var content = "";

        content += "<button><----</button><div>" + nameOftheMonth[month] + " " + year + "</div><button>----></button>"; 

        content += "<br/><table><tr>";                  
        for (count=0;count <= nameOftheDays.length-1; count++){

            content += "<td>" + nameOftheDays[count] + "</td>"; 

            if(count === nameOftheDays.length-1){
                content += "</tr><tr>";
            }
        }           
        while (numberOfDays > 0) {  
                content += "<td></td>";
                numberOfDays--;
        }

        while (num <= TotalNumOfDays){
            content += "<td>" + num + "</td>";
            if (num2 > 6) {
                num2 = 0;
                content += "</tr><tr>"
            }
            num2++;
            num++;              
        }   
        document.getElementById("calendar").innerHTML = content;
        document.getElementsByTagName("button")[0].setAttribute("id", "prevbutton");
        document.getElementsByTagName("button")[0].setAttribute("onclick", "prevButton()");     
        document.getElementsByTagName("button")[1].setAttribute("id", "nextButton");
        document.getElementsByTagName("button")[1].setAttribute("onclick", "nextButton()");
        document.getElementsByTagName("div")[1].setAttribute("id", "dateToday");

    }
    function nextButton(){
        if(month != null){
document.getElementById("calendar").innerHTML ="";
            month++;
            calendar()
        }
    }
</script>