I have a unique signature being generated for each iteration, which I want to eventually save on a .txt file.

My signature is quite simple, using 0-9 and A-Z, being 14 chars long.

I want to push it to an Array only if that Array doesn't contain it yet. Here is what I tried to do:

var uniqueSignature = []

do {
    var uniqueSignature = generateSignature()
    if (!signatureArray.includes(uniqueSignature)){ //checks if the Array does not contain the signature.
        signatureArray.push(uniqueSignature) //pushes the signature into the array.
    }
} while (!signatureArray.includes(uniqueSignature)) //Keep doing so until the signature can be inserted (meaning is unique)

function generateSignature(){
    var chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    var signatureLength = 14
    var genSignature = ""
    for (var i = 0; i <= signatureLength; i++) {
        var randomChars = Math.floor(Math.random() * chars.length)
        genSignature += chars.substring(randomChars, randomChars +1)
    }
    currentSignature = genSignature 
}

//[... eventually will write the array to a .txt files]

When I try to run it on Adobe Photoshop > Browse > Load script, I get this error:

I've also tried to replace .includes for .indexOf, pushing it only if signatureArray.indexOf(uniqueSignature) == -1, but got the same error.

Any ideas? I know that jsx/Photoshop has some limitations when it comes to code (like it won't let me use ${var} and such). Is that the thing here?

If so, is there any other way for me to achieve this push after verification?