@segment/analytics-next/src/lib/load-script.ts

Analytics Next (aka Analytics 2.0) is the latest version of Segment’s JavaScript SDK - enabling you to send your data to any tool without having to learn, test, or use a new API every time.

function findScript(src: string): HTMLScriptElement | undefined {
  const scripts = Array.prototype.slice.call(
    window.document.querySelectorAll('script')
  )
  return scripts.find((s) => s.src === src)
}

/**
 * Load a script from a URL and append it to the document.
 */
export function loadScript(
  src: string,
  attributes?: Record<string, string>
): Promise<HTMLScriptElement> {
  const found = findScript(src)

  if (found !== undefined) {
    const status = found?.getAttribute('status')

    if (status === 'loaded') {
      return Promise.resolve(found)
    }

    if (status === 'loading') {
      return new Promise((resolve, reject) => {
        found.addEventListener('load', () => resolve(found))
        found.addEventListener('error', (err) => reject(err))
      })
    }
  }

  return new Promise((resolve, reject) => {
    const script = window.document.createElement('script')

    script.type = 'text/javascript'
    script.src = src
    script.async = true

    script.setAttribute('status', 'loading')
    for (const [k, v] of Object.entries(attributes ?? {})) {
      script.setAttribute(k, v)
    }

    script.onload = (): void => {
      script.onerror = script.onload = null
      script.setAttribute('status', 'loaded')
      resolve(script)
    }

    script.onerror = (): void => {
      script.onerror = script.onload = null
      script.setAttribute('status', 'error')
      reject(new Error(`Failed to load ${src}`))
    }

    const firstExistingScript = window.document.querySelector('script')
    if (!firstExistingScript) {
      window.document.head.appendChild(script)
    } else {
      firstExistingScript.parentElement?.insertBefore(
        script,
        firstExistingScript
      )
    }
  })
}

export function unloadScript(src: string): Promise<void> {
  const found = findScript(src)

  if (found !== undefined) {
    found.remove()
  }

  return Promise.resolve()
}