var Cal = function(divId) {

        //Store div id
        this.divId = divId;

        // Days of week, starting on Sunday
        this.DaysOfWeek = [
            'Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'
        ];

        // Months, stating on January
        this.Months = ['January', 'February', 'March', 'April', 'May', 'June', 'July',
                            'August', 'September', 'October', 'November', 'December' ];

        // Set the current month, year
        var d = new Date();

        this.currMonth = d.getMonth();
        this.currYear = d.getFullYear();
        this.currDay = d.getDate();

        };

        // Goes to next month
        Cal.prototype.nextMonth = function() {
            if ( this.currMonth == 11 ) {
                this.currMonth = 0;
                this.currYear = this.currYear + 1;
            }
            else {
                this.currMonth = this.currMonth + 1;
            }
            this.showcurr();
        };

        // Goes to previous month
        Cal.prototype.previousMonth = function() {
            if ( this.currMonth == 0 ) {
                this.currMonth = 11;
                this.currYear = this.currYear - 1;
            }
            else {
                this.currMonth = this.currMonth - 1;
            }
            this.showcurr();
        };

        // Show current month
        Cal.prototype.showcurr = function() {
            this.showMonth(this.currYear, this.currMonth);
        };

        // Show month (year, month)
        Cal.prototype.showMonth = function(y, m) {

            var d = new Date()
            // First day of the week in the selected month
            , firstDayOfMonth = new Date(y, m, 1).getDay()
            // Last day of the selected month
            , lastDateOfMonth =  new Date(y, m+1, 0).getDate()
            // Last day of the previous month
            , lastDayOfLastMonth = m == 0 ? new Date(y-1, 11, 0).getDate() : new Date(y, m, 0).getDate();


            var html = '<table>';

            // Write selected month and year
            html += '<th><tr>';
            html += '<td colspan="7">' + this.Months[m] + ' ' + y + '</td>';
            html += '</tr></th>';


            // Write the header of the days of the week
            html += '<tr class="days">';
            for(var i=0; i < this.DaysOfWeek.length;i++) {
                html += '<td>' + this.DaysOfWeek[i] + '</td>';
            }
            html += '</tr>';

            // Write the days
            var i=1;
            do {

                var dow = new Date(y, m, i).getDay();

                // If Sunday, start new row
                if ( dow == 0 ) {
                html += '<tr>';
            }
            // If not Sunday but first day of the month
            // it will write the last days from the previous month
            else if ( i == 1 ) {
                html += '<tr>';
                var k = lastDayOfLastMonth - firstDayOfMonth+1;
                for(var j=0; j < firstDayOfMonth; j++) {
                    html += '<td class="not-current">' + k + '</td>';
                    k++;
                }
            }

            // Write the current day in the loop
            var chk = new Date();
            var chkY = chk.getFullYear();
            var chkM = chk.getMonth();
            if (chkY == this.currYear && chkM == this.currMonth && i == this.currDay) {
                html += '<td class="today">' + i + '</td>';
            } else {
                html += '<td class="normal">' + i + '</td>';
            }
            // If Saturday, closes the row
            if ( dow == 6 ) {
                html += '</tr>';
            }
            // If not Saturday, but last day of the selected month
            // it will write the next few days from the next month
            else if ( i == lastDateOfMonth ) {
                var k=1;
                for(dow; dow < 6; dow++) {
                    html += '<td class="not-current">' + k + '</td>';
                    k++;
                }
            }

            i++;
        }while(i <= lastDateOfMonth);

        // Closes table
        html += '</table>';

        // Write HTML to the div
        document.getElementById(this.divId).innerHTML = html;
    };

    // On Load of the window
    window.onload = function() {

        // Start calendar
        var c = new Cal("divCal");
        c.showcurr();

        // Bind next and previous button clicks
        getId('btnNext').onclick = function() {
            c.nextMonth();
        };
        getId('btnPrev').onclick = function() {
            c.previousMonth();
        };
    }

    // Get element by id
    function getId(id) {
        return document.getElementById(id);
    }



======================================================HTML==================================================

<div class="cal">
    <div class="calendar-wrapper">
    <input type="image" src="{% static '/images/previousButton.png' %}" id="btnPrev" width="25px">
    <input type="image" src="{% static '/images/nextButton.png' %}" id="btnNext" width="25px">
    <div id="divCal"></div>
</div>