Better decimal rounding about ember-math-helpers HOT 9 CLOSED

@Techn1x I could see that being useful. It's not supported by Math.round though.

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It is supported (kind of) by Number, though. (2.1254).toFixed(2) === '2.13'. Unfortunately (depending on use case), it also adds zeroes: (2).toFixed(2) === '2.00'

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@skeate should we have the round helper use Math.round unless you pass decimals, and if you specify decimals use toFixed?

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Also worth noting is that Number.toFixed() returns a string result, also it doesn't take into account values further on, for example (8.449).toFixed(1) === "8.4" whereas it should be 8.5?

I wrote this helper few weeks ago to solve the issue for myself. However if you do something like 8.449 rounded to 1 decimal place, it returns 8.4 (whereas it should return 8.5) so it's not entirely correct either, but if someone is clever enough to figure it out properly this might help;

import { helper } from '@ember/component/helper';

// Rounding decimal places since it doesn't seem to exist as a js math function, or as an ember-math-helpers helper
// NOTE: This will currently only work for decimals >= 0, with some work negative values could probably be supported

export function roundDecimal([value,decimals]) {

	if(!value || decimals < 0) return value;
	if(!decimals || decimals === 0) return Math.round(value);
	
	var sign = '-';

	return Number(Math.round(value + 'e' + decimals) + 'e' + sign + decimals);
}

export default helper(roundDecimal);

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Hopefully some combination of Math.round(), Number.toFixed() and my above code snippet will produce a correctly rounded result...

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8.449 should round to 8.4. Rounding does not take into account anything past the number after the cutoff.

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@Techn1x @skeate either of you guys interested in submitting a PR for this?

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@skeate oh haha my bad, you're right. Seems rounding is only supposed to look at the next number along and that's it. That being said, toFixed() still doesn't seem to work right.
For example, here's some funky answers I got;
(8.45).toFixed(1) === '8.4' (incorrect, should be 8.5)
(8.49).toFixed(1) === '8.5' (correct)
(8.65).toFixed(1) === '8.7' (correct)

(Just to be 100% sure I am now using this tool to double check my answers https://www.calculatorsoup.com/calculators/math/roundingnumbers.php )

@rwwagner90 I can probably write a PR for this this weekend, if no-one beats me to it

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That discrepancy is a result of the floating point representation of (e.g.) 8.45:

> 8.45 - 1
7.449999999999999

( - 1 because otherwise it'll just dutifully report "8.45")

There's a version that works here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/round#Decimal_rounding

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