I would like to render a JavaScript bigint
value to a string
in scientific notation.
I thought of Number.toExponential()
but it only works for numbers
.
const scientificNotation = n => parseInt(n).toExponential(); console.log(scientificNotation(prompt()));
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Answer
Intl does support Bigint:
Turns out BigInt.prototype.toLocaleString()
can be used with an options
for scientific-notation:
const fmt /*: BigIntToLocaleStringOptions */ = { notation: 'scientific', maximumFractionDigits: 20 // The default is 3, but 20 is the maximum supported by JS according to MDN. }; const b1 = 1234567890123456789n; console.log( b1.toLocaleString( 'en-US', fmt ) ); // "1.234567890123456789E18"
Original answer:
(This code is still useful for JS environments without Intl
support or if you need more than 20 digits of precision):
Because bigint
values are always integral, and because bigint.toString()
will return base-10 digits without further ceremony (other than a leading -
for negative values) then then a quick-and-dirty method is to take those rendered digits and insert a radix point (aka decimal dot) after the first digit and tack on the exponent at the end, and because it’s a base-10 string the exponent is the same as the length of the rendered string (neat, huh?)
function bigIntToExponential( value: bigint ): string { if( typeof value !== 'bigint' ) throw new Error( "Argument must be a bigint, but a " + ( typeof value ) + " was supplied." ); // const isNegative = value < 0; if( isNegative ) value = -value; // Using the absolute value for the digits. const str = value.toString(); const exp = str.length - 1; if( exp == 0 ) return ( isNegative ? "-" : '' ) + str + "e+0"; const mantissaDigits = str.replace( /(0+)$/, '' ); // Remove any mathematically insignificant zeroes. // Use the single first digit for the integral part of the mantissa, and all following digits for the fractional part (if any). let mantissa = mantissaDigits.charAt( 0 ); if( mantissaDigits.length > 1 ) { mantissa += '.' + mantissaDigits.substring( 1 ); } return ( isNegative ? "-" : '' ) + mantissa + "e+" + exp.toString(); } console.log( bigIntToExponential( 1n ) ); // "1e+0" console.log( bigIntToExponential( 10n ) ); // "1e+1" console.log( bigIntToExponential( 100n ) ); // "1e+2" console.log( bigIntToExponential( 1000n ) ); // "1e+3" console.log( bigIntToExponential( 10000n ) ); // "1e+4" console.log( bigIntToExponential( 1003n ) ); // "1.003e+3" console.log( bigIntToExponential( 10000000003000000n) ); // "1.0000000003e+16" console.log( bigIntToExponential( 1234567890123456789n ) ); // "1.234567890123456789e+18" console.log( bigIntToExponential( 12345678901234567898765432109876543210n ) ); // "1.234567890123456789876543210987654321e+37" console.log( bigIntToExponential( -1n ) ); // "-1e+0" console.log( bigIntToExponential( -10n ) ); // "-1e+1" console.log( bigIntToExponential( -100n ) ); // "-1e+2" console.log( bigIntToExponential( -1000n ) ); // "-1e+3"