Go's strconv.Unquote in TypeScript

✓ Verified: Go 1.23

How to use

Install via yarn add locutus and import: import { Unquote } from 'locutus/golang/strconv/Unquote'.

Or with CommonJS: const { Unquote } = require('locutus/golang/strconv/Unquote')

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	Unquote(`"hello"`)[0]	`'hello'`
2	Unquote(`'\\n'`)[0]	`'\n'`
3	Unquote(`'é'`)[0]	`'é'`

Notes

Interprets Go single-quoted, double-quoted, or backquoted string literals.
Returns [value, null] on success, [“”, error] on invalid syntax.

Here's what our current TypeScript equivalent to Go's strconv.Unquote looks like.

export function Unquote(s: string): [string, Error | null] {
  //      discuss at: https://locutus.io/golang/strconv/Unquote
  // parity verified: Go 1.23
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Interprets Go single-quoted, double-quoted, or backquoted string literals.
  //          note 2: Returns [value, null] on success, ["", error] on invalid syntax.
  //       example 1: Unquote(`"hello"`)[0]
  //       returns 1: 'hello'
  //       example 2: Unquote(`'\\n'`)[0]
  //       returns 2: '\n'
  //       example 3: Unquote(`'é'`)[0]
  //       returns 3: 'é'

  const input = String(s)
  if (input.length < 2) {
    return ['', new Error(`invalid syntax: ${input}`)]
  }

  const quote = input[0]
  const endQuote = input.at(-1)
  if (!quote || quote !== endQuote || (quote !== '"' && quote !== "'" && quote !== '`')) {
    return ['', new Error(`invalid syntax: ${input}`)]
  }

  const body = input.slice(1, -1)

  if (quote === '`') {
    return [body, null]
  }

  const [decoded, decodeError] = decodeGoEscapes(body)
  if (decodeError) {
    return ['', decodeError]
  }

  if (quote === "'" && Array.from(decoded).length !== 1) {
    return ['', new Error(`invalid rune literal: ${input}`)]
  }

  return [decoded, null]
}

const ESCAPE_MAP: Record<string, string> = {
  a: '\x07',
  b: '\b',
  f: '\f',
  n: '\n',
  r: '\r',
  t: '\t',
  v: '\v',
  '\\': '\\',
  "'": "'",
  '"': '"',
  '`': '`',
}

function isHex(char: string): boolean {
  return /[0-9a-fA-F]/.test(char)
}

function isOctal(char: string): boolean {
  return /[0-7]/.test(char)
}

function decodeGoEscapes(value: string): [string, Error | null] {
  let out = ''

  for (let i = 0; i < value.length; i++) {
    const char = value[i]
    if (char !== '\\') {
      out += char
      continue
    }

    const esc = value[i + 1]
    if (!esc) {
      return ['', new Error('invalid trailing backslash escape')]
    }

    const mapped = ESCAPE_MAP[esc]
    if (mapped !== undefined) {
      out += mapped
      i += 1
      continue
    }

    if (esc === 'x') {
      const hex = value.slice(i + 2, i + 4)
      if (hex.length !== 2 || !isHex(hex[0] ?? '') || !isHex(hex[1] ?? '')) {
        return ['', new Error(`invalid \\x escape: \\x${hex}`)]
      }
      out += String.fromCodePoint(Number.parseInt(hex, 16))
      i += 3
      continue
    }

    if (esc === 'u' || esc === 'U') {
      const width = esc === 'u' ? 4 : 8
      const hex = value.slice(i + 2, i + 2 + width)
      if (hex.length !== width || !/^[0-9a-fA-F]+$/.test(hex)) {
        return ['', new Error(`invalid \\${esc} escape: \\${esc}${hex}`)]
      }
      const codePoint = Number.parseInt(hex, 16)
      if (codePoint > 0x10ffff) {
        return ['', new Error(`invalid Unicode code point: ${hex}`)]
      }
      out += String.fromCodePoint(codePoint)
      i += 1 + width
      continue
    }

    if (isOctal(esc)) {
      let octal = esc
      let consumed = 1
      while (consumed < 3) {
        const next = value[i + 1 + consumed]
        if (!next || !isOctal(next)) {
          break
        }
        octal += next
        consumed += 1
      }

      out += String.fromCodePoint(Number.parseInt(octal, 8))
      i += consumed
      continue
    }

    return ['', new Error(`invalid escape sequence: \\${esc}`)]
  }

  return [out, null]
}

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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Help us add more

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Get inspiration from Go strings documentation, Go strings source, Go strings examples source, GopherJS.
Click "New file" in the appropriate folder on GitHub. This will fork the project to your account, directly add the file to it, and send a Pull Request to us.

We will then review it. If it's useful to the project and in line with our contributing guidelines your work will become part of Locutus and you'll be automatically credited in the authors section accordingly.

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