How to Map the Invoice lines to its SO lines via SuiteScript 2.0?

Hello. I'm running a script on the Invoice record. This script's aim is to take the value of the line field "custcol_altsales_invoice" from the invoice and map it to the corresponding SO line in a field called "custcol_ccaw_test_field_1". The issue is that this works if everything is invoiced at once (all the lines from the SO are present on the invoice). It will map incorrectly if, say, I only invoice some lines from the SO. Is there a way to map each line from the invoice to its exact line on the SO?

/**
 * @NApiVersion 2.x
 * @NScriptType UserEventScript
 * @NModuleScope SameAccount
 */
define(['N/record'], function(record) {


  function updateCommissionOnSalesOrder(context) {
    //only run if it's edit or create
    if (context.type == 'create' || context.type == 'edit') {
      //reference the current invoice
var invoiceRecord = context.newRecord;
      // Get the Sales Order ID from the Invoice record's "Created From" field
      var salesOrderId = invoiceRecord.getValue({ fieldId: 'createdfrom' });
      
      // Get the line count on the Invoice record
      var lineCount = invoiceRecord.getLineCount({
        sublistId: 'item'
      });


      // Update the "Commission Calculated" field on the