Check to see if attribute exists before creating one automatically

Ok, so I have the following set up to assign attributes to a new token automatically.


on("add:character", function(obj) {
});


The problem is, when ever a new sandbox spins up, it adds the attribute again. Making redundant copies. I don't want this, obviously. My solution thus far has been to disable the script. However, I want to add more tokens and characters now, and it keeps adding to those that already exist.

I've tried this,


on("add:character", function(obj) {
});


But this doesn't work. What do I need to do to simply check if the attribute already exists? obj.get() returns the value, so I checked it against FALSE 0, rather than "0" obviously. Would this work?

The error I get is:

ReferenceError: Invalid left-hand side in assignment at evalmachine.:3:5 at eval (


This makes me think it's a syntax error. I'm not familiar with JavaScript, I use LUA, and Perl.

In an add:character event, obj is the character object, not the attribute object. You'll want to find the attribute with the name "Strength" and a _characterid equal to obj.id, and check if that exists:

on('add:character', function (obj) {
    var strAttr = findObjs({
        _characterid: obj.id,
        name: 'Strength'
    })[0];
    // If the character doesn't have the Strength attribute, findObjs() will return a 0-length array.
    // The first element in a 0-length array (index 0) is undefined.
    // If the character has at least one Strength attribute, findObjs() will return an array with elements
    // and we assume the first element is the most relevant one
    
    if (!strAttr) { // `undefined` is a "falsey" value, so `!undefined` returns `true`
        // Create attribute Strength
    }
});

Because characters do not have a property named "Strength", obj.get("Strength") should be returning undefined. The exactly equal operator (===) compares both value and type, and undefined is not a numeric type, like 0.

Thank you, very much. I've only been working with Roll20's API and/or JS for 2 weeks.