Increment a number without getting rid of leading zeroes

Question

I am getting a value from database and I am reusing it as a number. This number has leading zeroes and it is limited to only 4 digits, meaning to say the format is 0001 or 0010 or 0100 or 1000. I am starting the count from zero when I add 1 to this number the leading zeroes are gone the way I add is for example

var databasevalue = 0000;
var incrementvalue = parseInt(databasevalue) + parseInt(1); 

Answer 1

Numbers don't have leading zeroes; that's a string thing.

If the value you're getting from the database is a string, you'll need to do this:

1. Get its length

2. Use parseInt(theString, 10) to parse it in base 10 (on some engines, a leading zero makes it think it should use base 8)

3. Add one to it (you never need to use parseInt on an actual number, so it's just + 1 not + parseInt(1))

4. Convert that into a string

5. Add zeroes to the beginning of the string in a loop until it's as long as the original

There's no built-in padding function that will do #5 for you, you either have to write one or do one of the hacks like theString = "00000000000000000000000".substr(theString.length - desiredLength) + theString (being sure that initial string has enough zeroes to cover what you want to cover).

Answer 2

I created a function today that you can use for that.

function incrementLeadingZeroNumber(leadingZeroString, amountToIncrement){
  var amountOfZerosToAdd = leadingZeroString.length;
  var stringToNumber = (+leadingZeroString);
  var zerosToAdd = new Array(amountOfZerosToAdd + 1).join( '0' );

  var zerosAndNewNumber = zerosToAdd + ( stringToNumber + amountToIncrement )
  var amountToSlice = (-1 * amountOfZerosToAdd)
  var newString = zerosAndNewNumber.slice(amountToSlice)
  return newString
}

//example usage
var incrementedNumber = incrementLeadingZeroNumber('0030', -10)

Answer 3

Here is a function you can use. min_size is the length of the string, so in your case '0000' min_size is 4. Your databasevalue starts at 0. The function converts the number to a string and checks the length of the string. Then it adds leading zeros till the min_size has been reached. The console.log shows the first following number '0001'. Here it's easy to change the amount of leading zeros.

var min_size = 4;
var start_value = 0;

function leading_zero (num) {
    var new_num = num.toString();
    for (var i = new_num.length; i < min_size; i++) {
        new_num = '0' + new_num;
    }
    return new_num;
}

console.log(leading_zero(start_value + 1));