Ruby's String.tr in TypeScript

How to use

Install via yarn add locutus and import: import { tr } from 'locutus/ruby/String/tr'.

Or with CommonJS: const { tr } = require('locutus/ruby/String/tr')

Use a bundler that supports tree-shaking so you only ship the functions you actually use. Vite, webpack, Rollup, and Parcel all handle this. For server-side use this is less of a concern.

Examples

These examples are extracted from test cases that automatically verify our functions against their native counterparts.

#	code	expected result
1	tr('hello', 'el', 'ip')	'hippo'
2	tr('abcxyz', 'a-z', 'A-Z')	'ABCXYZ'
3	tr('banana', 'an', 'o')	'booooo'

Ruby nil and TypeScript/JavaScript undefined

Ruby's nil and TypeScript/JavaScript undefined are semantically equivalent—both represent "no value" or "nothing here". However, they serialize differently: nil becomes null in JSON, while undefined is typically omitted or becomes undefined.

Locutus Ruby functions return undefined (idiomatic TypeScript/JavaScript) where Ruby would return nil. Our parity tests treat these as equivalent when verifying against native Ruby.

Notes

• Transliterate characters from from set to to set.

• Supports basic ranges like a-z; complement (^) is intentionally not implemented.

Here's what our current TypeScript equivalent to Ruby's String.tr looks like.

TSTypeScript JSJavaScript TSStandalone TS JSStandalone JS

Copy code

const expandTrSet = (pattern: string): string[] => {
  const chars = [...pattern]
  const expanded: string[] = []

  for (let i = 0; i < chars.length; i += 1) {
    const startChar = chars[i]
    if (startChar === undefined) {
      continue
    }

    if (i + 2 < chars.length && chars[i + 1] === '-') {
      const endChar = chars[i + 2]
      if (endChar !== undefined) {
        const startCode = startChar.codePointAt(0)
        const endCode = endChar.codePointAt(0)
        if (startCode !== undefined && endCode !== undefined) {
          const step = startCode <= endCode ? 1 : -1
          for (let code = startCode; step > 0 ? code <= endCode : code >= endCode; code += step) {
            expanded.push(String.fromCodePoint(code))
          }
          i += 2
          continue
        }
      }
    }

    expanded.push(startChar)
  }

  return expanded
}

export function tr(str: string, from: string, to: string): string {
  // parity verified: Ruby 3.3
  //      discuss at: https://locutus.io/ruby/String/tr/
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Transliterate characters from `from` set to `to` set.
  //          note 2: Supports basic ranges like `a-z`; complement (`^`) is intentionally not implemented.
  //       example 1: tr('hello', 'el', 'ip')
  //       returns 1: 'hippo'
  //       example 2: tr('abcxyz', 'a-z', 'A-Z')
  //       returns 2: 'ABCXYZ'
  //       example 3: tr('banana', 'an', 'o')
  //       returns 3: 'booooo'

  const source = String(str)
  const fromChars = expandTrSet(String(from))
  if (fromChars.length === 0) {
    return source
  }

  const toChars = expandTrSet(String(to))
  const map = new Map<string, string>()
  for (let index = 0; index < fromChars.length; index += 1) {
    const key = fromChars[index]
    if (key === undefined) {
      continue
    }
    const replacement = toChars.length === 0 ? '' : (toChars[Math.min(index, toChars.length - 1)] ?? '')
    map.set(key, replacement)
  }

  let out = ''
  for (const char of source) {
    out += map.has(char) ? (map.get(char) ?? char) : char
  }

  return out
}

const expandTrSet = (pattern) => {
  const chars = [...pattern]
  const expanded = []

  for (let i = 0; i < chars.length; i += 1) {
    const startChar = chars[i]
    if (startChar === undefined) {
      continue
    }

    if (i + 2 < chars.length && chars[i + 1] === '-') {
      const endChar = chars[i + 2]
      if (endChar !== undefined) {
        const startCode = startChar.codePointAt(0)
        const endCode = endChar.codePointAt(0)
        if (startCode !== undefined && endCode !== undefined) {
          const step = startCode <= endCode ? 1 : -1
          for (let code = startCode; step > 0 ? code <= endCode : code >= endCode; code += step) {
            expanded.push(String.fromCodePoint(code))
          }
          i += 2
          continue
        }
      }
    }

    expanded.push(startChar)
  }

  return expanded
}

export function tr(str, from, to) {
  // parity verified: Ruby 3.3
  //      discuss at: https://locutus.io/ruby/String/tr/
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Transliterate characters from `from` set to `to` set.
  //          note 2: Supports basic ranges like `a-z`; complement (`^`) is intentionally not implemented.
  //       example 1: tr('hello', 'el', 'ip')
  //       returns 1: 'hippo'
  //       example 2: tr('abcxyz', 'a-z', 'A-Z')
  //       returns 2: 'ABCXYZ'
  //       example 3: tr('banana', 'an', 'o')
  //       returns 3: 'booooo'

  const source = String(str)
  const fromChars = expandTrSet(String(from))
  if (fromChars.length === 0) {
    return source
  }

  const toChars = expandTrSet(String(to))
  const map = new Map()
  for (let index = 0; index < fromChars.length; index += 1) {
    const key = fromChars[index]
    if (key === undefined) {
      continue
    }
    const replacement = toChars.length === 0 ? '' : (toChars[Math.min(index, toChars.length - 1)] ?? '')
    map.set(key, replacement)
  }

  let out = ''
  for (const char of source) {
    out += map.has(char) ? (map.get(char) ?? char) : char
  }

  return out
}

Improve this function

Locutus is a community effort following The McDonald's Theory: we ship first iterations, hoping others will improve them. If you see something that could be better, we'd love your contribution.

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