How to Get the Last Digit of an Integer in JavaScript?

Getting the last digit of a JavaScript integer

In JavaScript, you can get the last digit of an integer in the following ways:

Using Remainder Operator

You can use the remainder operator (%) to get the last digit of an integer in the following way:

// ES6+
const lastDigit = (num) => num % 10;

console.log(lastDigit(0)); // 0
console.log(lastDigit(1234)); // 4
console.log(lastDigit(-1234)); // -4

In the example above, the remainder operator (%) works by dividing a given number by 10 and returning the remainder. It uses truncated division, and is equivalent to the following:

// ES6+
function lastDigit(num) {
    const quotient = Math.trunc(num / 10);
    return (num - (10 * quotient));
}

console.log(lastDigit(0)); // 0
console.log(lastDigit(1234)); // 4
console.log(lastDigit(-1234)); // -4

This works in the following way:

// num = 1234

// lastDigit = 1234 - (10 * Math.trunc(1234 / 10))
// lastDigit = 1234 - (10 * Math.trunc(123.4))
// lastDigit = 1234 - (10 * 123)
// lastDigit = 1234 - 1230
// lastDigit = 4

Converting to String and Retrieving Last Character

You could do the following:

  1. Convert the integer to a string;
  2. Get the last character of the string;
  3. Convert the string back to integer;
  4. Add negative sign to the last digit if integer was negative.
// ES13+
function lastDigit(num) {
    const numStr = num.toString();
    const lastChar = numStr.at(-1);
    const lastDigitUnsigned = Number.parseInt(lastChar, 10);

    return (num < 0) ? -lastDigitUnsigned : lastDigitUnsigned;
}

console.log(lastDigit(0)); // 0
console.log(lastDigit(1234)); // 4
console.log(lastDigit(-1234)); // -4

To support versions prior to ES13, you can use numStr[numStr.length - 1] instead of numStr.at(-1).


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