如何将 JavaScript BigInt 值转换为科学记数法?

How can I convert a JavaScript BigInt value to Scientific Notation?

我想用科学记数法将 JavaScript bigint 值呈现为 string

我想到了 Number.toExponential(),但它只适用于 numbers

const scientificNotation = n => parseInt(n).toExponential();

console.log(scientificNotation(prompt()));

Intl 是否 支持 Bigint:

事实证明 BigInt.prototype.toLocaleString() 可以与 options 一起用于科学记数法:

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" 

原回答:

(此代码对于没有 Intl 支持的 JS 环境或者需要超过 20 位精度的情况下仍然有用):

因为 bigint 值始终是整数,并且因为 bigint.toString() 将 return 以 10 为底的数字而无需进一步的仪式(负值的前导 - 除外)然后一个快速而肮脏的方法是采用那些呈现的数字并在第一个数字之后插入一个小数点(又名小数点)并在最后加上指数,因为这是一个以 10 为基数的字符串,指数与渲染字符串的长度相同(整洁,是吧?)

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"