如何获取给定月份的上个月名称（用文字而不是数值）？

Question

我想要一个函数，它可以给出任何给定月份的上个月的全名[不仅仅是当前月份] 例如：prevMonth(August) = July; prevMonth(January)= December.

我是 js 新手，不知道如何使用这个数组来获取结果：

monthsarray: ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]

Answer 1

function prevMonth(month) {
    const index = monthsarray.indexOf(month);
    if (index > 0) {
        return monthsarray[index - 1];
    }
    if (index === 0) {
        return monthsarray[monthsarray.length - 1];
    }
    throw new Error('Invalid Month given');
}

Answer 2

期待这样的简单解决方案吗？

var monthsarray = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]

function prevMonth(curMonth) {

  var curMonthIndex = monthsarray.indexOf(curMonth);
  var prevMonthIndex;
  if (curMonthIndex == 0) prevMonthIndex = monthsarray.length - 1;
  else if (curMonthIndex == monthsarray.length - 1) prevMonthIndex = 0;
  else prevMonthIndex = curMonthIndex - 1;

  return monthsarray[prevMonthIndex];
}


console.log(prevMonth("August"));
console.log(prevMonth("December"));

Answer 3

let monthsarray1= ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"] ;

let m="May";

console.log(pvsMonth(m))


function pvsMonth(m){

    let ln=monthsarray1.length

   

    let idx=monthsarray1.indexOf(m)

 
    
    if(idx==0){
    return  monthsarray1[ln-1]
    }else{
        return  monthsarray1[idx-1]
    
    }
}

如何获取给定月份的上个月名称（用文字而不是数值）？

How to get previous month name on given some month (in words not numerical value)?

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