I'm using Intl.NumberFormat
to format numbers:
const formatter = new Intl.NumberFormat('en-US', {
minimumFractionDigits: 1,
maximumFractionDigits: 4,
minimumSignificantDigits: 1,
maximumSignificantDigits: 4
})
formatter.format(0.99999) // results: '1'. desired result: '0.9999'
formatter.format(0.006393555) // results: '0.006394'. desired result: '0.006393'
formatter.format(0.9972620384752073) // results: '0.9973'. desired result: '0.9972'
formatter.format(12345.67) // results: '12,350'. desired result: '12,345.67'
formatter.format(200001) // results: '200,000'. desired result: '200,001'
As you can see the numbers are being rounded automatically, which is undesirable behavior in my case.
Is there a way to tell the formatter not to round? I Didn't found any option or combination of options to achieve that.
The Intl. NumberFormat() object enables language-sensitive number formatting. We can use this to convert currency, numbers, percentages, units, and other notation into formatted strings. This is particularly useful in eCommerce applications, with examples like displaying an item price or recipt printing.
There are certain rules to follow when rounding a decimal number. Put simply, if the last digit is less than 5, round the previous digit down. However, if it's 5 or more than you should round the previous digit up. So, if the number you are about to round is followed by 5, 6, 7, 8, 9 round the number up.
The maximum number of significant digits for the number formatter.
JavaScript numbers can be formatted in different ways like commas, currency, etc. You can use the toFixed() method to format the number with decimal points, and the toLocaleString() method to format the number with commas and Intl. NumberFormat() method to format the number with currency.
NumberFormat will always round up, but you can play around this one extra function.
function roundDownSignificantDigits(number, decimals) {
let significantDigits = (parseInt(number.toExponential().split('e-')[1])) || 0;
let decimalsUpdated = (decimals || 0) + significantDigits - 1;
decimals = Math.min(decimalsUpdated, number.toString().length);
return (Math.floor(number * Math.pow(10, decimals)) / Math.pow(10, decimals));
}
and then
const formatter = new Intl.NumberFormat('en-US', {
minimumFractionDigits: 1,
maximumFractionDigits: 4,
minimumSignificantDigits: 1,
maximumSignificantDigits: 4
})
result:
formatter.format(roundDownSignificantDigits(0.99999,4)); // "0.9999"
formatter.format(roundDownSignificantDigits(0.006393555,4)); // "0.006393"
formatter.format(roundDownSignificantDigits(0.9972620384752073,4)); // "0.9972"
I don't think this is possible with current spec and there are few proposals for the new spec, but you can still use formatToParts
method and add custom function to format number parts as you wish.
For your first use case it could look something like:
const trauncateFractionAndFormat = (parts, digits) => {
return parts.map(({ type, value }) => {
if (type !== 'fraction' || !value || value.length < digits) {
return value;
}
let retVal = "";
for (let idx = 0, counter = 0; idx < value.length && counter < digits; idx++) {
if (value[idx] !== '0') {
counter++;
}
retVal += value[idx];
}
return retVal;
}).reduce((string, part) => string + part);
};
const formatter = new Intl.NumberFormat('en-US', {
minimumFractionDigits: 0,
maximumFractionDigits: 20
})
console.log(trauncateFractionAndFormat(formatter.formatToParts(0.99999), 4));
console.log(trauncateFractionAndFormat(formatter.formatToParts(0.006393555), 4));
console.log(trauncateFractionAndFormat(formatter.formatToParts(0.9972620384752073), 4));
console.log(trauncateFractionAndFormat(formatter.formatToParts(12345.67), 4));
console.log(trauncateFractionAndFormat(formatter.formatToParts(20001), 4));
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