fromFormat as the opposite to toFormat

[claudemartin]

I can't find an easy way to parse a string that was created using toFormat. I'd like to see a fromFormat function that does that (based on current configuration) and additionally an option to configure BigNumber to automatically parse the strings passed to the constructor. Something like this: BigNumber.config({ AUTO_PARSE: true });

Does this exist yet? In my case this is only about ignoring the groupSeparator and reading decimalSeparator as '.'. But it would also have to handle everything else in BigNumber.Format.

[shuckster]

Does this work for you?

function removeFormatting ({ fromNumberString, withDecimalPoint = '.' }) {
  const rx = new RegExp(`[^${withDecimalPoint}\\d]*`, 'g')
  return fromNumberString.replace(rx, '')
}

removeFormatting({ fromNumberString: '123 456 789.12345 6789' })
// 123456789.123456789

It works by creating a regular-expression that removes everything that isn't a digit or a decimal-point.

[MikeMcl]

I don't want to enhance the BigNumber constructor so it can handle toFormat strings, but following shuckster a fromFormat function could be added using, for example

// Assumes '-' is only used as a minus sign.
BigNumber.fromFormat = (stringFromToFormat, formatObject) => {
  const sep = formatObject.decimalSeparator;
  const str = stringFromToFormat.replace(new RegExp(`[^${sep || '.'}\\d-]+`, 'g'), '');
  return new BigNumber(sep ? str.replace(sep, '.') : str); 
};  

(If this function was internal to the library then obviously it would have access to the global FORMAT object and so it wouldn't need to be passed in.)

[claudemartin]

I agree that the constructor doesn't need to be changed. But a fromFormat like this would be nice. Note it should also allow e as in BigNumber.fromFormat("1e-3") and everything in ALPHABET. And then there's ±Infinity and NaN. It should be able to handle anything that toFormat could possibly return but also everything the constructor would allow. Pre- and suffix could be removed to prevent problems with them containing digits, especially in combination with a custom alphabet.

[povilass]

probably should be called fromFormat -> parse
parse('1000.000-e', {format: '', groupSeparator, ...etc})
parse('1000.000-e')