这里有一个稍微不同的方法(我不认为其他答案会这样做)。我不确定我是喜欢还是讨厌它，但它确实有效!

export function addDaySuffix(day: number) { 
  const suffixes =
      '  stndrdthththththththththththththththththstndrdthththththththst';
    const startIndex = day * 2;

    return `${day}${suffixes.substring(startIndex, startIndex + 2)}`;
  }

序数函数的另一个版本可以如下所示:

function toCardinal(num) {
    var ones = num % 10;
    var tens = num % 100;

    if (tens < 11 || tens > 13) {
        switch (ones) {
            case 1:
                return num + "st";
            case 2:
                return num + "nd";
            case 3:
                return num + "rd";
        }
    }

    return num + "th";
}

变量的命名更加明确，使用驼峰大小写约定，并且可能更快。

规则如下:

St用于以1结尾的数字(例如1st，发音为first) Nd与以2结尾的数字连用(例如92nd，发音为ninety-second) Rd与以3结尾的数字连用(例如33rd，发音为33third) 作为上述规则的例外，所有以11、12或13结尾的“青少年”数字都使用-th(例如，11，发音为111,112， 读作一百零十二位) Th用于所有其他数字(例如:9th，发音为ninth)。

以下JavaScript代码(在14年6月重写)实现了这一点:

function ordinal_suffix_of(i) {
    var j = i % 10,
        k = i % 100;
    if (j == 1 && k != 11) {
        return i + "st";
    }
    if (j == 2 && k != 12) {
        return i + "nd";
    }
    if (j == 3 && k != 13) {
        return i + "rd";
    }
    return i + "th";
}

0-115之间数字的示例输出:

  0  0th
  1  1st
  2  2nd
  3  3rd
  4  4th
  5  5th
  6  6th
  7  7th
  8  8th
  9  9th
 10  10th
 11  11th
 12  12th
 13  13th
 14  14th
 15  15th
 16  16th
 17  17th
 18  18th
 19  19th
 20  20th
 21  21st
 22  22nd
 23  23rd
 24  24th
 25  25th
 26  26th
 27  27th
 28  28th
 29  29th
 30  30th
 31  31st
 32  32nd
 33  33rd
 34  34th
 35  35th
 36  36th
 37  37th
 38  38th
 39  39th
 40  40th
 41  41st
 42  42nd
 43  43rd
 44  44th
 45  45th
 46  46th
 47  47th
 48  48th
 49  49th
 50  50th
 51  51st
 52  52nd
 53  53rd
 54  54th
 55  55th
 56  56th
 57  57th
 58  58th
 59  59th
 60  60th
 61  61st
 62  62nd
 63  63rd
 64  64th
 65  65th
 66  66th
 67  67th
 68  68th
 69  69th
 70  70th
 71  71st
 72  72nd
 73  73rd
 74  74th
 75  75th
 76  76th
 77  77th
 78  78th
 79  79th
 80  80th
 81  81st
 82  82nd
 83  83rd
 84  84th
 85  85th
 86  86th
 87  87th
 88  88th
 89  89th
 90  90th
 91  91st
 92  92nd
 93  93rd
 94  94th
 95  95th
 96  96th
 97  97th
 98  98th
 99  99th
100  100th
101  101st
102  102nd
103  103rd
104  104th
105  105th
106  106th
107  107th
108  108th
109  109th
110  110th
111  111th
112  112th
113  113th
114  114th
115  115th

以前我为我的东西做的…

function convertToOrdinal(number){
    if (number !=1){
        var numberastext = number.ToString();
        var endchar = numberastext.Substring(numberastext.Length - 1);
        if (number>9){
            var secondfromendchar = numberastext.Substring(numberastext.Length - 1);
            secondfromendchar = numberastext.Remove(numberastext.Length - 1);
        }
        var suffix = "th";
        var digit = int.Parse(endchar);
        switch (digit){
            case 3:
                if(secondfromendchar != "1"){
                    suffix = "rd";
                    break;
                }
            case 2:
                if(secondfromendchar != "1"){
                    suffix = "nd";
                    break;
                }
            case 1:
                if(secondfromendchar != "1"){
                    suffix = "st";
                    break;
                }
            default:
                suffix = "th";
                break;
         }
            return number+suffix+" ";
     } else {
            return;
     }
}

通过将数字分成一个数组并反转，我们可以很容易地使用数组[0]和数组[1]检查数字的最后两位数字。

如果一个数字是十位数数组[1]= 1，它需要“th”。

function getDaySuffix(num)
{
    var array = ("" + num).split("").reverse(); // E.g. 123 = array("3","2","1")
    
    if (array[1] != "1") { // Number is not in the teens
        switch (array[0]) {
            case "1": return "st";
            case "2": return "nd";
            case "3": return "rd";
        }
    }
    
    return "th";
}

我为更大的数字和所有测试用例写了这个函数

function numberToOrdinal(num) {
    if (num === 0) {
        return '0'
    };
    let i = num.toString(), j = i.slice(i.length - 2), k = i.slice(i.length - 1);
    if (j >= 10 && j <= 20) {
        return (i + 'th')
    } else if (j > 20 && j < 100) {
        if (k == 1) {
            return (i + 'st')
        } else if (k == 2) {
            return (i + 'nd')
        } else if (k == 3) {
            return (i + 'rd')
        } else {
            return (i + 'th')
        }
    } else if (j == 1) {
        return (i + 'st')
    } else if (j == 2) {
        return (i + 'nd')
    } else if (j == 3) {
        return (i + 'rd')
    } else {
        return (i + 'th')
    }
}