code: function stringToFunction(str) {
    // immediate such as "> 20"
    if (/^ *\W+/.test(str)) return new Function('_', 'return _ ' + str);
  
    // properties such as "name.first" or "age > 18"
    var fn = new Function('_', 'return _.' + str);
    return fn
  }
docs: Convert property `str` to a function.
  
  @param {String} str
  @return {Function}
  @api private