Question

How to count the number of digits in an integer with JavaScript

Answer 1

function countDigitsString(value) {
  // Convert the number to a string
  const text = String(value);

  // If negative, ignore the leading '-'
  if (text.startsWith("-")) {
    return text.length - 1;
  }

  return text.length;
}

const number1 = -12345;
const digits1 = countDigitsString(number1);

console.log("Number:", number1);
console.log("Digit count (String method):", digits1);


/*
run:

Number: -12345
Digit count (String method): 5

*/

 

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Answer 2

function countDigitsLog10(value) {
  const num = Math.abs(value);

  // Zero must be handled explicitly
  if (num === 0) {
    return 1;
  }

  // Use floor(log10(n)) + 1
  return Math.floor(Math.log10(num)) + 1;
}

const number2 = 987654321;
const digits2 = countDigitsLog10(number2);

console.log("Number:", number2);
console.log("Digit count (log10 method):", digits2);


/*
run:

Number: 987654321
Digit count (log10 method): 9

*/

 

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