So basically my issue is that I'm looking to get some data from an object. The object is picked from and html tag and the selected option is put into a function. The function handles getting the data but throws an error when trying to get the length of an array found inside the object. getRandInRange is a function I created that works perfectly so that is not the issue.

When I run the code in the browser this is the error I get

Uncaught TypeError: Cannot read properties of undefined (reading 'length')
    at buildHorde (app.js:46:60)
    at setValue (app.js:33:5)
    at HTMLInputElement.onclick (index.html:27:101)

function buildHorde(obj,num){
    // for every num add a random coin roll
    for (i = 0; i < num; i ++){
        coinArr.push(obj.coins[getRandInRange(0, obj.coins.length-1)]);
    }
    // following lines add the new arrays into the html document.
    document.getElementById("coins").innerHTML = coinArr;
    return;
}

<p>Select Party Level: <select name="Party Level" id="getObj">
    <option value=level1>level1</option>
    <option value=level2>level2</option>
</select></p>

And this is the code to set the arguments in the function

function setValue(){
    var select = document.getElementById('getObj');
    obj = select.options[select.selectedIndex].value
    num = document.getElementById('getNum').value;
    buildHorde(obj,num);
}

level1 object

let level1 = {
    coins: ["No coin", getRandInRange(1,6) * 1000 + " Copper Pieces ", getRandInRange(1,8) * 100 + " Silver Pieces ", getRandInRange(1,4) * 10 + " Platinum Pieces "],
    goods: ["nothing ", "Extravagant painting ", "ornate statue "],
    items: ["Boots of speed ", mundane.weapon[getRandInRange(0, mundane.weapon.length-1)], "Potion of fire breathing "],
}