Date enforcer dependent on jquery and moment

date_enforcer.js

var dateEnforcer = function (startDate, endDate) {

    $(startDate).on('focus', function () {
        this.previousDate =  moment(this.value).format('MM-DD-YYYY');
    }).change(function(){
        var newDate = moment(this.value).format('MM-DD-YYYY');
        var endDateMoment =  moment($(endDate).val()).format('MM-DD-YYYY');

        if (this.previousDate != 'Invalid date'){
           if (moment(newDate).isAfter(endDateMoment)){
                $(endDate).val(newDate);
           }
        } else {
            $(endDate).val(newDate);
        }
    });

    $(endDate).on('focus', function () {
        this.previousDate =  moment(this.value).format('MM-DD-YYYY');
    }).change(function(){
        var newDate = moment(this.value).format('MM-DD-YYYY');
        var startDateMoment =  moment($(startDate).val()).format('MM-DD-YYYY');

        if (this.previousDate != 'Invalid date'){
           if (moment(newDate).isBefore(startDateMoment)){
                $(startDate).val(newDate);
           }
        } else {
            $(startDate).val(newDate);
        }
    });
};

dateEnforcer('#id_from_date', '#id_to_date');

This compares dates so that if you're using a calendar widget and are having a date that has a range that it should apply to, this will ensure you can't flip the range accidentally.