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

Question

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.

You obviously need a third-party arbitrary precision library. Are you using an environment where you can install one, such as Node? — Álvaro González, Apr 25 '17 at 15:05
@SebastiánPalma won't work, numbers are too big. MAX_SAFE_INTEGER in JavaScript is 9007199254740991. — Jared Smith, Apr 25 '17 at 15:06
For a string that big you have to use a library for precision, but normally you can cast your string as number `Number(message)` — Lixus, Apr 25 '17 at 15:07
@hindmost won't work for arbitrary additions, wonder if that's what the OP wants? — Jared Smith, Apr 25 '17 at 15:11
[This question](http://stackoverflow.com/questions/4985153/large-numbers-to-string-in-javascript) might help you, OP. — Yassine Badache, Apr 25 '17 at 15:12
@Jared Smith Work for given question. Nobody knows what the OP actually wants — hindmost, Apr 25 '17 at 15:13
Possible duplicate of [Large numbers to string in JavaScript](http://stackoverflow.com/questions/4985153/large-numbers-to-string-in-javascript) — Jared Smith, Apr 25 '17 at 15:13
Surely arbitrary addition can be assumed as a requirement. I mean, otherwise `return "12345612345678901234567891"` would count as "answering the question". — Daniel Beck, Apr 25 '17 at 15:15

Blue · Accepted Answer · 2018-12-27T03:25:54.793

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>

edited Dec 27 '18 at 03:25

answered Apr 25 '17 at 15:05

Blue

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Can i do this without library?? – Brothers Apr 25 '17 at 15:48
No, you can't (Unless you take bits and pieces from the library and rewrite it yourself). This is not something that supported by normal javascript. – Blue Apr 25 '17 at 15:50
I already done with this library but i want to do it without library support. – Brothers Apr 25 '17 at 16:59
Well then you should have asked that question instead. – Blue Apr 25 '17 at 17:14
@KevinPatel _"Can i do this without library??"_ Yes, it is possible derive correct sum without a library. You can segment initial string into `.length`s of `3` within an array, determine if number to add added to segment of three is greater than `1000`. If `true`, increment previous segment of `3` by `1`, set current segment of `3` to `000`. The approach can be adjusted to add appropriate number to previous index of array, and current array, to sum to, for example, `5123` if adding `124` to `4999`. See approach at Answer – guest271314 Apr 25 '17 at 17:33
1

Since 2019, there is support for `BigInt` in most browsers. That means you can accomplish this with `(BigInt(123122348903) + BigInt(1)).toString()` – joshnuss Jul 18 '21 at 12:22

score 2 · Answer 2 · answered Jul 30 '22 at 10:57

2

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

answered Jul 30 '22 at 10:57

Kamil Naja

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guest271314 · Answer 3 · 2017-04-25T17:37:16.450

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)
);

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

3 Answers3

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