uppy/packages/@uppy/dashboard/src/utils/copyToClipboard.js

/**
 * Copies text to clipboard by creating an almost invisible textarea,
 * adding text there, then running execCommand('copy').
 * Falls back to prompt() when the easy way fails (hello, Safari!)
 * From http://stackoverflow.com/a/30810322
 *
 * @param {String} textToCopy
 * @param {String} fallbackString
 * @return {Promise}
 */
module.exports = function copyToClipboard (textToCopy, fallbackString) {
  fallbackString = fallbackString || 'Copy the URL below'

  return new Promise((resolve) => {
    const textArea = document.createElement('textarea')
    textArea.setAttribute('style', {
      position: 'fixed',
      top: 0,
      left: 0,
      width: '2em',
      height: '2em',
      padding: 0,
      border: 'none',
      outline: 'none',
      boxShadow: 'none',
      background: 'transparent'
    })

    textArea.value = textToCopy
    document.body.appendChild(textArea)
    textArea.select()

    const magicCopyFailed = () => {
      document.body.removeChild(textArea)
      window.prompt(fallbackString, textToCopy)
      resolve()
    }

    try {
      const successful = document.execCommand('copy')
      if (!successful) {
        return magicCopyFailed('copy command unavailable')
      }
      document.body.removeChild(textArea)
      return resolve()
    } catch (err) {
      document.body.removeChild(textArea)
      return magicCopyFailed(err)
    }
  })
}