JavaScript / reactJS - round up last decimal (without hardcoded decimal to calculate)

Question

By using JavaScript to calculate, For Example (in live can be any value)

1000/0.997 = 1003.0090270812437

By using PC calculator to calculate

1000/0.997 = 1003.009027081244 // auto round up last decimal

But if !!! this is correct and same as window, in this situation no need round up

500/0.997 = 501.5045135406219 // this is correct and same as window calculator

My prefer output is the auto round up value 1003.009027081244

Question: In JavaScript, how to round up the last digit of decimal?

What I have tried:

Math.round(1003.0090270812437) // 1003

@Wazeed your suggestion is hardcoded `12` , have to avoid hardcoded — FeelRightz, Oct 08 '21 at 12:35

score 0 · Answer 1 · edited Oct 08 '21 at 12:35

0

const result = Number((1000/0.997).toPrecision(16))

const result = Number((1000 / 0.997).toPrecision(16))
console.log(result)

edited Oct 08 '21 at 12:35

DecPK

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answered Oct 08 '21 at 12:33

anmatika

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why using `16` ? – FeelRightz Oct 08 '21 at 12:37
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toPrecision – anmatika Oct 08 '21 at 12:39
how do you know taking `16` as value ? – FeelRightz Oct 08 '21 at 12:43
because in live example, will facing any number with different decimal, and needed to auto round up last decimal, `16` is kind a hardcode – FeelRightz Oct 08 '21 at 12:47
@FeelRightz, Microsoft Windows OS Calc application is giving 16 precision results. Hence to get the same results as Windows OS Calc in Javascript, this can be used. 1054/100, for this Calc will not perform round-up for last decimal – Wazeed Oct 08 '21 at 12:51
@Wazeed how to get `16` ? or dynamic get `16` ? – FeelRightz Oct 08 '21 at 12:59

Tom · Answer 2 · 2021-10-10T16:28:34.937

0

There is no nice javascript way that I know to achieve this. Due to my knowledge this is the way to go:

Math.round(1003.0090270812437*1000000000000)/1000000000000

Edit: If you do not want to round to a fixed number of decimals, then I would write a little function to count the given decimals before to know your exponent of 10:

var countDecimals = function(value) {
    if (Math.floor(value) !== value)
        return value.toString().split(".")[1].length || 0;
    return 0;
}

var temp = Math.pow(10, countDecimals-1);
Math.round(1003.0090270812437*temp)/temp;

edited Oct 10 '21 at 16:28

answered Oct 08 '21 at 12:34

Tom

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yes, unless you know is using `1000000000000` – FeelRightz Oct 08 '21 at 12:39

Dimitar · Answer 3 · 2021-10-08T13:58:44.733

0

Option 1: playing with numbers and decimals

const countDecimals = value => {
  let text = value.toString()
  if (text.indexOf('e-') > -1) {
    let [base, trail] = text.split('e-')
    let deg = parseInt(trail, 10)
    return deg - 1
  }

  if (Math.floor(value) !== value) return value.toString().split(".")[1].length - 1 || 0

  return 0
}
const round = number => Math.round(number * Math.pow(10, countDecimals(number - 1))) / Math.pow(10, countDecimals(number - 1))

Option 2: playing with strings

let round = number => {
  let str = (number).toString()
  let [num, dec] = str.split(".")
  let leading_zeros = ""
  for (const char of dec) {
    if (char !== '0') break
    leading_zeros += '0'
  }
  dec = Math.round(parseFloat(dec.substring(0, dec.length - 1) + "." + dec[dec.length - 1])).toString()
  return parseFloat(num + "." + leading_zeros + dec)
}

edited Oct 08 '21 at 13:58

answered Oct 08 '21 at 13:03

Dimitar

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how to get decimal place ? because it can be any decimal place – FeelRightz Oct 08 '21 at 13:04
@FeelRightz https://stackoverflow.com/a/27082406/12182781 – Dimitar Oct 08 '21 at 13:05
By combining my rounding function and @Alex Filatov 's decimal counting function you can solve your problem. – Dimitar Oct 08 '21 at 13:07
@FeelRightz there I did the integration for you. – Dimitar Oct 08 '21 at 13:10
i try using `1003.0090270812437` , output still `1003.0090270812437` – FeelRightz Oct 08 '21 at 13:14
and what do you want the output to be? – Dimitar Oct 08 '21 at 13:15
`1003.009027081244` as question explained – FeelRightz Oct 08 '21 at 13:16
can you explain why need to deduct 1 ? – FeelRightz Oct 08 '21 at 13:22
Because you want to round up the second last decimal place, you need to round to the N-1 decimal place not to Nth decimal place since rounding up to the Nth decimal place will just return the input. You can now do something yourself and modify the code so that you can round up to N - M decimal places. Now give me my reputation and have a nice day. – Dimitar Oct 08 '21 at 13:24
thx for your answer, but it wont work if `500/0.997`, see my updated question – FeelRightz Oct 08 '21 at 13:28
I just thought of another way to do this using strings. convert float to string, get the second string (decimal numbers), add a decimal on the N-1 place so if you had 123.4567 now your decimal string is 456.7 then you convert decimal string to float and round it, then convert it back to a string, add it to 123 and add a decimal between both to get 123.457 and convert that string to float. – Dimitar Oct 08 '21 at 13:30
`501.5045135406219` is correct and no need to do anything, but `1003.0090270812437` need to be roundup – FeelRightz Oct 08 '21 at 13:32
`501.5045135406219` last digit is 9, but no need round up – FeelRightz Oct 08 '21 at 13:33
I added another option – Dimitar Oct 08 '21 at 13:47
option 2 , sadly if `1000/0.997` , wont work – FeelRightz Oct 08 '21 at 13:50
Try the new edit solution should work for both cases – Dimitar Oct 08 '21 at 13:59
wont work on `500/0.997` – FeelRightz Oct 08 '21 at 14:13
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/237961/discussion-between-dimitar-veljanovski-and-feelrightz). – Dimitar Oct 08 '21 at 14:14

score 0 · Answer 4 · answered Oct 08 '21 at 13:26

0

Maybe you could use string based solution

Convert a decimal number to string, then split it by the .. Then take a decimal part length substracted by 1, and use it in toFixed on the original number.

You will probably need some additional checks, to see if there is a decimal part of a number

const decimal = 1003.0090270812437;
const text = decimal.toString().split('.')[1];

console.log(decimal.toFixed(text.length - 1)); // 1003.009027081244

answered Oct 08 '21 at 13:26

Terminat

1,199
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this wont work if calculation go to `500/0.997`, see my question – FeelRightz Oct 08 '21 at 13:37
Please update a question title. You don't want a last digit rounded up. You want a PC calculator behaviour of rounding up numbers – Terminat Oct 08 '21 at 13:38

score -1 · Answer 5 · answered Oct 08 '21 at 12:35

-1

You can just use toFixed(${Amount of decimals you want to show})

Example: (2321/912).toFixed(1) will show one fraction of the decimal number

(2322/ 1232).toFixed((2322/ 1232).toString().length - 1 ) will round you up the last digit

answered Oct 08 '21 at 12:35

MrCeRaYA

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JavaScript / reactJS - round up last decimal (without hardcoded decimal to calculate)

5 Answers5