Map Item with Variable from Array Index - Javascript

Question

I'm working w/ Excel Tables in JS and trying to find a way to set/manipulate the column order before pasting data into table vs after. There is a line w/ .map that seems to be key, but I can't seem to use/pass variables inside it.

How can I access HeaderRowArr[1] inside the map? In the end, I'll want to iterate over the entire HeaderRowArr and map each item, but I feel like if I can get this first part done, that should hopefully be clearer.

This line is the line I'm working on:

var newData = transactions.map(item => [item.MERCHANT, item.HeaderRowArr[1], item.CATEGORY, item.AMOUNT]);

But I get error: "Unable to get property '1' of undefined or null reference"

Full Snippet:

export async function helloworld(event) {
    try {
        await Excel.run(async (context) => {
            //Start Func

            var transactions = [
                {
                    "BoxLabel": "AB12345678R001-005",
                    "MERCHANT": "The Phone Company",
                    "CATEGORY": "Communications",
                    "AMOUNT": "120"
                },
                {
                    "BoxLabel": "ZY12345678R001-005",
                    "MERCHANT": "Southridge Video",
                    "CATEGORY": "Entertainment",
                    "AMOUNT": "40"
                }
            ];

            var WSNameStr = "Workorder_Samples";
            var ws = await Get_WorkSheet(context, false, WSNameStr)

            var TBLNameStr = "ExpensesTable";
            var rng = ws.getRangeByIndexes(0, 0, 1, Object.keys(transactions[0]).length)
            var expensesTable = await Get_Table(context, false, ws, TBLNameStr, rng)

            //expensesTable.getHeaderRowRange().values = [Object.keys(transactions[0])];
            var HeaderRowArr = ["MERCHANT", "BoxLabel", "CATEGORY", "AMOUNT"]
            expensesTable.getHeaderRowRange().values = [HeaderRowArr];

            //var newData = transactions.map(item => [item.CATEGORY, item.BoxLabel, item.MERCHANT, item.AMOUNT]); //This controls body output order, doesn't track headers order
            console.log(HeaderRowArr[1])
            var newData = transactions.map(item => [item.MERCHANT, item.BoxLabel, item.CATEGORY, item.AMOUNT]);
            //var newData = transactions.map(item => [item.MERCHANT, item.HeaderRowArr[1], item.CATEGORY, item.AMOUNT]);

            expensesTable.rows.add(null, newData);
         
            ws.activate();
            //End Func
            await context.sync();
        });
    } catch (error) {
        console.error(error);
    }
    event.completed();
}