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I have some data like RM 28.51 (Currency), RM30.28(Currency) in my table and need to use these data to do some calculation

my solution is to parseFloat(28.51).tofixed(2) + parseFloat(30.28).tofixed(2)

but when the moment more and more data come in , sometimes they will some decimal point error shown as result

Example my result at the end will show 3859.39 but the actual is 3859.40

Is there any better solution?

Hong Ernest
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    `parseFloat(28.51).tofixed(2) + parseFloat(30.28).tofixed(2)` - this won't add the numbers because `.toFixed()` returns a string. Also why do you call `parseFloat()` with numbers? – Andreas Mar 03 '22 at 08:28
  • The more single rounded numbers you add the bigger the loss of data becomes. If table refers to an actual database, I recommend to do your calculations on it as well. – Lain Mar 03 '22 at 08:34
  • above is some example, sometimes the data is string. so as @Lain mention, I cant use parseFloat.toFixed right – Hong Ernest Mar 03 '22 at 08:35
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    or should I use Math.round(someNumber * 1e2) / 1e2 instead of var someNumber = 123.456; someNumber = parseFloat(someNumber.toFixed(2)); – Hong Ernest Mar 03 '22 at 08:38
  • One ancient way used to be a multiplication to whole numbers and division back to decimals. Like `(parseFloat('28.51')*1000 + parseFloat('30.28')*1000)/1000`. – Lain Mar 03 '22 at 08:39
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    You should not use floating-point number if you want to represent decimals: [Why not use Double or Float to represent currency?](https://stackoverflow.com/questions/3730019/why-not-use-double-or-float-to-represent-currency) – t.niese Mar 03 '22 at 09:18

1 Answers1

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parseFloat(28.51).toFixed(2) + parseFloat(30.28).toFixed(2) - sometimes they will some decimal point error shown as result

The JavaScript toFixed method takes in a number and outputs a string

When you use + with two numbers, you add both numbers.

When you use + with two strings, you join both strings together.

The example below illustrates the difference.

function addTwoStrings(value1, value2) {
  return parseFloat(value1).toFixed(2) + parseFloat(value2).toFixed(2)
}
function addTwoNumbers(value1, value2) {
  return (parseFloat(value1) + parseFloat(value2)).toFixed(2)
}

console.log(addTwoStrings(28.514, 30.284))
console.log(addTwoNumbers(28.514, 30.284))
Zach Jensz
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  • I think OP's problem is more to do with floating point precision in JavaScript. – phuzi Mar 03 '22 at 08:54
  • @phuzi Oops read *that* wrong – Zach Jensz Mar 03 '22 at 08:56
  • ```const value1 = 28.51 const value2 = '30.28' const value3 = +value1 + +value2 function valueToCurrencyString(value) { return parseFloat(value).toLocaleString('en', { minimumFractionDigits: 2, maximumFractionDigits: 2, style: 'currency', currency: 'MYR' }); } console.log(valueToCurrencyString(value3)); newNumber = parseFloat(value3).toFixed(2); console.log(newNumber); ``` sorry am a newbie, but is that newNumber any dffirence with console.log(valueToCurrencyString(value3)); – Hong Ernest Mar 03 '22 at 08:59
  • Sorry @HongErnest I don't understand that question – Zach Jensz Mar 03 '22 at 09:01
  • ohh sorry, I means If I parseFloat(value3).toFixed(2), what is the difference to console.log(valueToCurrencyString(value3)); – Hong Ernest Mar 03 '22 at 09:04
  • @HongErnest I have massively improved the answer please take another read :) – Zach Jensz Mar 03 '22 at 09:14