Passing an object with a custom toString() as a 'class' attribute

I am writing a library using objects with a custom toString() method to render class names. Simplified example:

const object = {
  toString() {
    return computeClassNames();
  },
  //  ... other data
};

element.className = object;

It works great on plain DOM and React, but can’t work with Preact because if a class attribute is an object, it will use the object enumerable keys associated with a truthy value to format the classname.

I understand why you chose to do this, and I find it quite useful. But would you consider changing the condition to format the class objects to something like:

if (lastSimple && lastSimple.toString === Object.prototype.toString) {
    attributes.class = hashToClassName(lastSimple);
}

or (might be more robust)

if (lastSimple && String(lastSimple) === '[object Object]') {
    attributes.class = hashToClassName(lastSimple);
}

or (not the cleanest but might be more efficient)

if (lastSimple && Object.prototype.toString.call(lastSimple) === '[object Object]') {
    attributes.class = hashToClassName(lastSimple);
}

I could change my library to return an object with keys as class names, but I’d prefer not to add code specific to preact.

Thank you

[developit]

Absolutely, should be seeing this land very soon. Cheers!

[developit]

We can definitely remove the object check, that’ll save bytes and it’s actually totally superficial - it was added to avoid setting <div foo="[object Object]">, but doing so isn’t really an issue.

The function check is to prevent this, so we’ll likely want to keep it: