Go's url.JoinPath in TypeScript

✓ Verified: Go 1.23

How to use

Install via yarn add locutus and import: import { JoinPath } from 'locutus/golang/url/JoinPath'.

Or with CommonJS: const { JoinPath } = require('locutus/golang/url/JoinPath')

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	`JoinPath('https://locutus.io/api/', 'v1', 'users')`	`'https://locutus.io/api/v1/users'`
2	`JoinPath('https://locutus.io/api/v1?x=1', '..', 'v2')`	`'https://locutus.io/api/v2?x=1'`
3	`JoinPath('/a/b/', '../c')`	`'/a/c'`

Notes

Joins and cleans URL path elements while preserving query/fragment for absolute URLs.

Here's what our current TypeScript equivalent to Go's url.JoinPath looks like.

const cleanPath = (path: string): string => {
  if (path === '') {
    return '.'
  }

  const rooted = path.startsWith('/')
  const segments = path.split('/')
  const stack: string[] = []

  for (const segment of segments) {
    if (segment === '' || segment === '.') {
      continue
    }

    if (segment === '..') {
      const top = stack[stack.length - 1]
      if (top && top !== '..') {
        stack.pop()
      } else if (!rooted) {
        stack.push('..')
      }
      continue
    }

    stack.push(segment)
  }

  const cleaned = `${rooted ? '/' : ''}${stack.join('/')}`
  if (cleaned === '') {
    return rooted ? '/' : '.'
  }

  return cleaned
}

const joinPathParts = (parts: string[]): string => {
  if (parts.every((part) => part === '')) {
    return ''
  }

  return cleanPath(parts.join('/'))
}

export function JoinPath(base: string, ...elem: string[]): string {
  //      discuss at: https://locutus.io/golang/url/JoinPath
  // parity verified: Go 1.23
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Joins and cleans URL path elements while preserving query/fragment for absolute URLs.
  //       example 1: JoinPath('https://locutus.io/api/', 'v1', 'users')
  //       returns 1: 'https://locutus.io/api/v1/users'
  //       example 2: JoinPath('https://locutus.io/api/v1?x=1', '..', 'v2')
  //       returns 2: 'https://locutus.io/api/v2?x=1'
  //       example 3: JoinPath('/a/b/', '../c')
  //       returns 3: '/a/c'

  const baseValue = String(base)
  const parts = [baseValue, ...elem.map((part) => String(part))]

  try {
    const url = new URL(baseValue)
    const joinedPath = joinPathParts([url.pathname, ...elem.map((part) => String(part))])
    url.pathname = joinedPath === '' ? '/' : joinedPath.startsWith('/') ? joinedPath : `/${joinedPath}`
    return url.toString()
  } catch {
    return joinPathParts(parts)
  }
}

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

Got a rainy Sunday afternoon and a taste for a porting puzzle?

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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