ArbitraryBase.js

/**
* Converts a string from one base to other
* @param {string} stringInBaseOne String in input base
* @param {string} baseOneCharacters Character set for the input base
* @param {string} baseTwoCharacters Character set for the output base
* @returns {string}
*/
const convertArbitraryBase = (stringInBaseOne, baseOneCharacters, baseTwoCharacters) => {
 if ([stringInBaseOne, baseOneCharacters, baseTwoCharacters].map(arg => typeof arg).some(type => type !== 'string')) {
 throw new TypeError('Only string arguments are allowed')
 }
 [baseOneCharacters, baseTwoCharacters].forEach(baseString => {
 const charactersInBase = [...baseString]
 if (charactersInBase.length !== new Set(charactersInBase).size) {
 throw new TypeError('Duplicate characters in character set are not allowed')
 }
 })
 const reversedStringOneChars = [...stringInBaseOne].reverse()
 const stringOneBase = baseOneCharacters.length
 let value = 0
 let placeValue = 1
 for (const digit of reversedStringOneChars) {
 const digitNumber = baseOneCharacters.indexOf(digit)
 if (digitNumber === -1) {
 throw new TypeError(`Not a valid character: ${digit}`)
 }
 value += (digitNumber * placeValue)
 placeValue *= stringOneBase
 }
 let stringInBaseTwo = ''
 const stringTwoBase = baseTwoCharacters.length
 while (value > 0) {
 const remainder = value % stringTwoBase
 stringInBaseTwo = baseTwoCharacters.charAt(remainder) + stringInBaseTwo
 value /= stringTwoBase
 }
 const baseTwoZero = baseTwoCharacters.charAt(0)
 return stringInBaseTwo.replace(new RegExp(`^${baseTwoZero}+`), '')
}

export { convertArbitraryBase }

// > convertArbitraryBase('98', '0123456789', '01234567')
// '142'

// > convertArbitraryBase('98', '0123456789', 'abcdefgh')
// 'bec'

// > convertArbitraryBase('129', '0123456789', '01234567')
// '201'