How to increment a string in Javascript

Question

Let's say I have the following string:

aRandomString

I'm then checking my database to see if that string has been used before (or if there's any string that starts with the given one). If it has, I'd like to increment it. The result would be the following:

aRandomString1

If that string exists, it would become aRandomString2, and so on. I'm assuming I need to complete the following steps: 1. Check for trailing numbers or set to 0, 2. Increment those trailing numbers by 1, append that number to the original string. Just trying to figure out a solid way to accomplish this!

Update

This is what I have so far:

var incrementString = function( str ){
    var regexp = /\d+$/g;
    if( str.match(regexp) )
    {
        var trailingNumbers = str.match( regexp )[0];
        var number = parseInt(trailingNumbers);
        number += 1;

        // Replace the trailing numbers and put back incremented
        str = str.replace(/\d+$/g , '');
        str += number;
    }else{
        str += "1";
    }
    return str;
}

I feel like this should be easier though.

@NickONeill If there can be numbers in other parts of the string, then you should probably choose a character unique from any other characters that the string can contain, and use that to separate your string from the incremental number at the end. That way you won't confuse it if you have a string that, without the incrementing number, is of the form x123 (where 123 can be confused with the incrementing number that you'll stick on the end). — ajp15243
– ajp15243, Commented Jan 14, 2014 at 19:43

adamduren · Accepted Answer · 2014-01-14 21:26:06Z

9

function incrementString(str) {
  // Find the trailing number or it will match the empty string
  var count = str.match(/\d*$/);

  // Take the substring up until where the integer was matched
  // Concatenate it to the matched count incremented by 1
  return str.substr(0, count.index) + (++count[0]);
};

If the match is the empty string, incrementing it will first cast the empty string to an integer, resulting the value of 0. Next it preforms the increment, resulting the value of 1.

answered Jan 14, 2014 at 21:26

adamduren

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3 Comments

Nick ONeill Over a year ago

Wow, this was incredibly elegant!

Sir Montes Over a year ago

But in the case of input string with zero prefix e.g. 001 not working properly...

Justin Over a year ago

updated @adamduren 's answer to handle leading zeros, below is for number with 3 digits, e.g. 001 return str.substr(0, count.index) + ("000" + (++count[0])).slice(-3);

Gabriel GUERIN · Accepted Answer · 2021-02-23 13:28:23Z

5

I had to keep the leading zeros in the number, this is how I did it:

function incrementString (string) {  
  // Extract string's number
  var number = string.match(/\d+/) === null ? 0 : string.match(/\d+/)[0];
  
  // Store number's length
  var numberLength = number.length

  // Increment number by 1
  number = (parseInt(number) + 1).toString();
  
  // If there were leading 0s, add them again
  while (number.length < numberLength) {
    number = "0" + number;
  }
    
  return string.replace(/[0-9]/g, '').concat(number);
}

answered Feb 23, 2021 at 13:28

Gabriel GUERIN

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Comments

Bob Siefkes · Accepted Answer · 2023-06-16 09:58:48Z

0

Incrementing string with support for padding zeros A001 will become A002. And support for plain string ABC will become ABC1. And adding digits when needed: ABC9 will become ABC10. I've used simular function for invoice number incremention.

  const incrementNr = (nr) => {
    const [nrDigits] = /\d*$/.exec(nr);
    const next = '' + (+nrDigits + 1);
    const nextNr = nr.slice(0, nr.length - Math.min(next.length, nrDigits.length)) + next;
    return nextNr;
  };```

answered Jun 16, 2023 at 9:58

Bob Siefkes

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