Appending Suffix to Numbers in JavaScript

Appending suffixes to numbers in JavaScript is used to add ordinal indicators (like "st", "nd", "rd", and "th") to the end of a number to denote its position in a sequence. This is useful for displaying dates, rankings, or other numeric data.

A custom function can be created to append the correct suffix to a given number.

The function handles special cases for numbers ending in 11, 12, and 13, and applies the appropriate suffix based on the last digit for other numbers.

Rules for Ordinal Suffixes

The task of our function is to append 'st', 'nd', 'rd', 'th' to the number according to the following rules:

• st is used with numbers ending in 1 (e.g. 1st, 21st, 101st)
• nd is used with numbers ending in 2 (e.g. 2nd, 22nd, 102nd)
• rd is used with numbers ending in 3 (e.g. 3rd, 23rd, 103rd)
• Exception: Numbers ending with 11, 12, or 13 always use th (e.g. 11th, 12th, 13th, 111th, 112th, 113th)
• th is used for all other numbers (e.g. 4th, 5th, 9th, 20th)

Sample Input:

const num = 4513;

Sample Output:

4513th

Explanation: Even though 4513 ends with 3, the last two digits form 13, which is an exception case that must be appended with "th".

Algorithm Implementation

Here's the core function that determines the correct suffix for any number:

function getOrdinalSuffix(num) {
    // Handle zero as special case
    if (num === 0) return "";
    
    // Check for teen exceptions (11, 12, 13, 111, 112, 113, etc.)
    if (num % 100 === 11 || num % 100 === 12 || num % 100 === 13) {
        return "th";
    }
    
    // Check last digit for regular cases
    const lastDigit = num % 10;
    if (lastDigit === 1) return "st";
    if (lastDigit === 2) return "nd";
    if (lastDigit === 3) return "rd";
    
    // Default case
    return "th";
}

function appendSuffix(num) {
    return num + getOrdinalSuffix(num);
}

// Test the function
console.log(appendSuffix(1));    // 1st
console.log(appendSuffix(2));    // 2nd
console.log(appendSuffix(3));    // 3rd
console.log(appendSuffix(11));   // 11th
console.log(appendSuffix(21));   // 21st
console.log(appendSuffix(113));  // 113th

1st
2nd
3rd
11th
21st
113th

Example: Single-Digit Numbers

Let's test our function with single-digit numbers from 1 to 9:

const appendText = (num = 1) => {
    let suffix = "th";
    if (num === 0) suffix = "";
    if (num % 10 === 1 && num % 100 !== 11) suffix = "st";
    if (num % 10 === 2 && num % 100 !== 12) suffix = "nd";
    if (num % 10 === 3 && num % 100 !== 13) suffix = "rd";
    
    return num + suffix;
};

const singleDigits = [1, 2, 3, 4, 5, 6, 7, 8, 9];
singleDigits.forEach(num => console.log(appendText(num)));

1st
2nd
3rd
4th
5th
6th
7th
8th
9th

Example: Special Teen Cases

The teen numbers (11, 12, 13) and their multiples (111, 112, 113, etc.) are exceptions that always use "th":

const appendText = (num = 1) => {
    let suffix = "th";
    if (num === 0) suffix = "";
    if (num % 10 === 1 && num % 100 !== 11) suffix = "st";
    if (num % 10 === 2 && num % 100 !== 12) suffix = "nd";
    if (num % 10 === 3 && num % 100 !== 13) suffix = "rd";
    
    return num + suffix;
};

const teenNumbers = [11, 12, 13, 111, 112, 113, 211, 212, 213];
teenNumbers.forEach(num => console.log(appendText(num)));

11th
12th
13th
111th
112th
113th
211th
212th
213th

Example: Mixed Large Numbers

Testing with various large numbers to demonstrate the function works correctly across different ranges:

const appendText = (num = 1) => {
    let suffix = "th";
    if (num === 0) suffix = "";
    if (num % 10 === 1 && num % 100 !== 11) suffix = "st";
    if (num % 10 === 2 && num % 100 !== 12) suffix = "nd";
    if (num % 10 === 3 && num % 100 !== 13) suffix = "rd";
    
    return num + suffix;
};

const mixedNumbers = [21, 22, 23, 101, 102, 103, 121, 122, 123, 1001];
mixedNumbers.forEach(num => console.log(appendText(num)));

21st
22nd
23rd
101st
102nd
103rd
121st
122nd
123rd
1001st

Practical Use Cases

Here are some common scenarios where ordinal suffixes are useful:

function formatDate(day, month, year) {
    const months = ['January', 'February', 'March', 'April', 'May', 'June',
                   'July', 'August', 'September', 'October', 'November', 'December'];
    
    const appendText = (num) => {
        let suffix = "th";
        if (num % 10 === 1 && num % 100 !== 11) suffix = "st";
        if (num % 10 === 2 && num % 100 !== 12) suffix = "nd";
        if (num % 10 === 3 && num % 100 !== 13) suffix = "rd";
        return num + suffix;
    };
    
    return `${months[month - 1]} ${appendText(day)}, ${year}`;
}

console.log(formatDate(1, 1, 2024));   // January 1st, 2024
console.log(formatDate(22, 12, 2023)); // December 22nd, 2023
console.log(formatDate(13, 6, 2024));  // June 13th, 2024

January 1st, 2024
December 22nd, 2023
June 13th, 2024

Conclusion

Appending ordinal suffixes to numbers in JavaScript requires handling special cases for teen numbers (11, 12, 13) while applying standard rules for other digits. This functionality is essential for creating user-friendly displays of rankings, dates, and sequential data.