JSFiddle - React, Tailwind, and code Playground

JavaScript

const content = `4624    
An account was successfully logged on.
Subject:
    Security ID:        NT AUTHORITY\SYSTEM
    Account Name:       SERVER$
    Account Domain:     COMPANY
    Logon ID:       0x3E7

Logon Information:
    Logon Type:     7
    Restricted Admin Mode:  -
    Virtual Account:        No
    Elevated Token:     No

New Logon:
    Security ID:        COMPANY\Susan
    Account Name:       SUSAN
    Account Domain:     COMPANY
    Logon ID:       0x3ED0915C
    Linked Logon ID:        0x0
    Network Account Name:   -
    Network Account Domain: -
    Logon GUID:     {7bac704d-8521-0b5e-4548-5c61a3614dc0`;
function getDetails(value) {
  var lines = value.split("\n");
  var accountName = "- not found -";
  var loginType = "- not found -";
  var sourceIp = "- not found -";
  // store the count of how many you have found while iterating
  let accountsFound = 0;
  lines.forEach(function(line) {
    // just split each line on the : and trim each part to avoid all the substrings
  	let key, value;
    [key, value] = line.trim().split(':');
    if (key !== undefined) {
    	key = key.trim();
    }
    
    if (value !== undefined) {
      value = value.trim();
    }
    // console.log(key, value);
    if (key === "Logon Type") {
      loginType = value;
    } 
    if (key === "Account Name") {
     if (accountsFound === 1) {
      accountName = value;
     }
     // keep track of how many you have found so far
     accountsFound++;
    } 
    if (key === "Source Network Address") {
      sourceIp = value;
    }
  });
  return  loginType + " " + accountName + " " + sourceIp;
}

console.log(getDetails(content));