Javascript Code 128 String Builder - Ascii Value> 127 issue

Question

I've been trying to build a small html/javascript based code 128 type B text builder.

I have it working for most barcodes, but I'm running into an issue if the value used creates a checksum that is a character that is greater than ascii 127. I'm not sure what I should be using to replace that value in that case. I've read of adding 'Code 3' and 'FNC X' values in the barcode, but it's not clear in what format, with braces and should FNC be 'FNC4' or 'FNC 4', or if that is relevant to the checksum.

I'm using the free 128 font from this site, http://jtbarton.com/Barcodes/BarcodeStringBuilderExample.aspx . I've tried various conditions, such as if the value is >127, take the existing ascii value instead of adding 32, but the barcode is then not readable.

I have a jsfiddle here, https://jsfiddle.net/jcqvag5g/ . If you use a value like 500.77005.YELLO.XXXXX.0160828, the barcode text is invalid.

Any insight would be appreciated. I haven't found a working solution at the moment. It could also be the specific barcode font I'm using, so recommendations for other solid 128 fonts would also be appreciated.

This is the main js code.

function textTo128(str) {
    /*
     * Generate 128 Barcode text, suitable for copying and pasting.
     */
        var len         = str.length; //str.length - get length of string, used to generate the checksum.
        var type128     = 104; // 128 Type B start
        var typeClose   = 106;
        var total       = 104; 

        var i; // Counter Variable
        for(i=0;i<len;i++){
            total += ((i+1) * (str.charCodeAt(i)-32)); //Multiply char position with decimal value of character, keep running total
        }

        var modVal      = total % 103; // Use Modulus to find our checksum
        var checksum    = String.fromCharCode(modVal+32);

        if(modVal+32>126){alert(modVal+32);};
        document.getElementById('barcodeTotal').innerHTML = String.fromCharCode(type128+100) + str + checksum + String.fromCharCode(typeClose+100);
    }

Thanks, -David

Answer 1

checksum should add 18 if larger than 126

var checksum = String.fromCharCode(modVal+32 > 126 ? modVal+32+18 : modVal+32);