计算两个日期之间的天数精确到 .5？

看了下你的描述，你想要的是这样一个效果？

function getDays(startDate,endDate) {
    var days = 0;
    var startInfo = startDate.split(' '),
        endInfo = endDate.split(' '),
        
        startDay = new Date(startInfo[0]),
        endDay = new Date(endInfo[0]), 
        
        endHour = endInfo[1].split(':')[0]
    
    if( startDay.getTime() != endDay.getTime()) {
        days = (endDay.getTime() - startDay.getTime()) / 86400000
    }

    if(endHour <= 12) {
        days += 0.5
    } else {
        days += 1
    }
    return days
}