How do I add 1 to a big integer represented as a string in JavaScript? - Stack Overflow

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How do I add 1 to this string in JavaScript?

var message = "12345612345678901234567890";

I want the output like this:

"12345612345678901234567891"

I tried this:

var message = "12345612345678901234567890";
message = parseInt(message);
var result = message + 1;

But parseInt returned a value in scientific notation like 1.234567896453e+25.

How do I add 1 to this string in JavaScript?

var message = "12345612345678901234567890";

I want the output like this:

"12345612345678901234567891"

I tried this:

var message = "12345612345678901234567890";
message = parseInt(message);
var result = message + 1;

But parseInt returned a value in scientific notation like 1.234567896453e+25.

• javascript

Share Improve this question Follow edited Apr 26, 2017 at 4:03 Pang 10.1k146146 gold badges8686 silver badges124124 bronze badges asked Apr 25, 2017 at 15:03 BrothersBrothers 9911 silver badge88 bronze badges 13

• You obviously need a third-party arbitrary precision library. Are you using an environment where you can install one, such as Node? – Álvaro González Commented Apr 25, 2017 at 15:05
• 1 parseInt(message) + 1 isn't it? – Sebastián Palma Commented Apr 25, 2017 at 15:06
• 4 @SebastiánPalma won't work, numbers are too big. MAX_SAFE_INTEGER in JavaScript is 9007199254740991. – Jared Smith Commented Apr 25, 2017 at 15:06
• 2 This question might help you, OP. – Yassine Badache Commented Apr 25, 2017 at 15:12
• 2 Possible duplicate of Large numbers to string in JavaScript – Jared Smith Commented Apr 25, 2017 at 15:13

 |  Show 8 more ments

3 Answers 3

Sorted by: Reset to default 8

Try the big integer library BigInteger.js to add large numbers.

var message = "12345612345678901234567890";

var messageAsNumber = bigInt(message);
var messagePlusOne = messageAsNumber.add('1');

console.log(messagePlusOne.toString());

<script src="https://peterolson.github.io/BigInteger.js/BigInteger.min.js"></script>

There is no need to use libraries (2022), you can just use JS BigInt object

let message = "12345612345678901234567890";
let messageBigInt = BigInt(message);
console.log(messageBigInt + BigInt(1)); // 12345612345678901234567891n

You can create an array from the string in .lengths of 3 beginning from the end of the string.

Use a pattern which checks if adding 1 would result in the index of the array as a number would sum to 1000, if true, increment previous array index by 1 and fill the current array index with "000".

The pattern below only checks and adjusts last two elements of array; the same pattern can be extended to check each index of array, to properly adjust one or more of the indexes to "000" and increment the previous index by 1.

let message1 = "12345612345678901234567890";
let message2 = "12345612345678901234567999";
let message3 = "12345612345678901234999999";

function addNumberToString(str, numToAdd, digits = []) {

  const [N, len, max] = [3, str.length, 1000];

  for (let i = -N, l = len; digits.length < len / N; i -= N, l -= N) {
    digits.unshift(str.slice(i, l));
  }

  function add(m) {
    if (+digits[digits.length - m] + numToAdd < max) {
      let n = +digits[digits.length - m];
      digits[digits.length - m] = String(Number(n + numToAdd));
    } else {
      const M = m + 1;
      if (+digits[digits.length - M] + numToAdd < max) {
        let n = +digits[digits.length - M];
        digits[digits.length - M] = String(Number(n + numToAdd));
        digits[digits.length - (M - 1)] = "0".repeat(N);
      } else {
          if (digits[digits.length - (m + 1)]) {
            digits[digits.length - (M - 1)] = "0".repeat(N);
            add(m + 1);
          }
      }
    }
    return digits.join("")
  }
  return add(1);

}

console.log(
  addNumberToString(message1, 1)   
, addNumberToString(message2, 1)
,  addNumberToString(message3, 1)
);

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