GA4 Session ID Parsing Function

parseGa4SessionId.js

const parseGa4SessionId = (str) => {
  
  let value;
  const parts = str.split('.');
  
  const parser = {
    v1: (str) => {
      let parsed = {};
      const data = str.split('.').slice(2);
      
      let indexMap = {
        0: 's',
        1: 'o',
        2: 'g',
        3: 't',
        4: 'j',
        5: 'l',
        6: 'h',
      };
      
      data.forEach((value, index) => {
      	parsed[indexMap[index]] = value;
      });
      
      return parsed;
    },
    v2: (str) => {
      let parsed = {};
      const data = str.split('.').slice(2).join('');
      
      let keyMap = {};
      
      data.split('$').forEach((segment) => {
      	let prefix = segment[0];
      	let key = keyMap[prefix] || prefix;
      	parsed[key] = segment.substring(1);
      });
      
      return parsed;
    },
  };
  
  if (parts[0].indexOf('GS') === 0) {
  
    value = parser[{
      GS1: 'v1',
      GS2: 'v2',
    }[parts[0]]](str);
    
  } else {
    
    if (str.indexOf('$') > -1) {
      str = 'GS2.' + str;
      value = parser.v2(str);
    } else {
      str = 'GS1.' + (parts.length == 2 ? '1.' : '') + str;
      value = parser.v1(str);
    }
    
  }
  
  return value;
  
};

Assumes an ID following any of the following the formats:

GS1.1.1746270489.2.1.1746270616.60.0.0
GS2.1.s1746270489$o2$g1$t1746270616$j60$l0$h0
1746270489.2

1746270489.2 assuming it has been parsed to pull only the [SessionID].[SessionNumber] segments. It would be wise to wrap any call to this method in a try/catch to avoid any errors. This method doesn't cover other possible pre-parsed values.