text: //  json2.js
  //  2017-06-12
  //  Public Domain.
  
  const rx_one = /^[\],:{}\s]*$/
  const rx_two = /\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g
  const rx_three = /"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g
  const rx_four = /(?:^|:|,)(?:\s*\[)+/g
  const rx_escapable = /[\\"\u0000-\u001f\u007f-\u009f\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g
  const rx_dangerous = /[\u0000\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g
  
  export const jsonParser = function (text, reviver) {
    let j
    function walk(holder, key) {
      // The walk method is used to recursively walk the resulting structure so
      // that modifications can be made.
      let k
      let v
      const value = holder[key]
      if (value && typeof value === 'object') {
        for (k in value) {
          if (Object.prototype.hasOwnProperty.call(value, k)) {
            v = walk(value, k)
            if (v !== undefined) {
              value[k] = v
            } else {
              delete value[k]
            }
          }
        }
      }
      return reviver.call(holder, key, value)
    }
    // Parsing happens in four stages. In the first stage, we replace certain
    // Unicode characters with escape sequences. JavaScript handles many characters
    // incorrectly, either silently deleting them, or treating them as line endings.
    text = String(text)
    rx_dangerous.lastIndex = 0
    if (rx_dangerous.test(text)) {
      text = text.replace(rx_dangerous, a => '\\u' + ('0000' + a.charCodeAt(0).toString(16)).slice(-4))
    }
    // In the second stage, we run the text against regular expressions that look
    // for non-JSON patterns. We are especially concerned with "()" and "new"
    // because they can cause invocation, and "=" because it can cause mutation.
    // But just to be safe, we want to reject all unexpected forms.
  
    // We split the second stage into 4 regexp operations in order to work around
    // crippling inefficiencies in IE's and Safari's regexp engines. First we
    // replace the JSON backslash pairs with "@" (a non-JSON character). Second, we
    // replace all simple value tokens with "]" characters. Third, we delete all
    // open brackets that follow a colon or comma or that begin the text. Finally,
    // we look to see that the remaining characters are only whitespace or "]" or
    // "," or ":" or "{" or "}". If that is so, then the text is safe for eval.
    if (
      rx_one.test(
        text
          .replace(rx_two, '@')
          .replace(rx_three, ']')
          .replace(rx_four, '')
      )
    ) {
      // In the third stage we use the eval function to compile the text into a
      // JavaScript structure. The "{" operator is subject to a syntactic ambiguity
      // in JavaScript: it can begin a block or an object literal. We wrap the text
      // in parens to eliminate the ambiguity.
      j = eval('(' + text + ')')
      // In the optional fourth stage, we recursively walk the new structure, passing
      // each name/value pair to a reviver function for possible transformation.
      return (typeof reviver === 'function')
        ? walk({ '': j }, '')
        : j
    }
    throw new SyntaxError('JSON.parse')
  }
  