JavaScript .length not working?!?

[dpjollygreen]

So my site is a type of gaming environment for showcasing my kids art and practicing my own skills. It has a virtual shop and inventory that I populate using a series of the below, one for each item. It is an exact duplicate (aside from nomenclature) as one that is known to work, the rope. Short of it is I've used this exact technique for items that are working, but this one I traced back to this point using well placed innerHTML lines... I think.

////////////////////////////////////////////////////////////////////////////

     if(inventory.includes("Helmet")){

        const helmetString = /Helmet/g;

        const helmetP2String = /Helmet_/g;

    

        const matchHelmet = inventoryString.match(helmetString);

        const matchHelmetP2 = inventoryString.match(helmetP2String);

    

//Problem area

       document.getElementById("test").innerHTML = inventory;

        let num1 = matchHelmet.length;

        let num2 = matchHelmetP2.length;

        document.getElementById("test2").innerHTML = inventory;

 //Problem area



         let numHelmet = num1 - num2;

      

        for(let i = 0; i < numHelmet; i++){

            let helmet = document.createElement('li');

            let helmetLink = document.createElement('a');

            helmetLink.textContent = "Helmet";

            helmetLink.href = "javascript:sellHelmet()";

            helmet.appendChild(helmetLink);

            listInv.appendChild(helmet);

        }

     }

///////////////////////////////////////////////////////////////////////

My troubleshooting toolkit is limited so any assistance or advise you might have is greatly appreciated.

 

[dpjollygreen]

Assume the item is in the list. Of the two test lines the first is being populated.

 

[dpjollygreen]

This problem has been solved. helmetP2String was not in the inventory and caused a runtime error. Had to check for null value before trying to use it in .length.