No, that was never good.
We are wanting to supply a single value for the container property. Here is what that init function does with the container property.
config.containers = document.querySelectorAll(selectors.container);
The init function uses the container property to assign a list of matching elements as containers.
The container property is a string that is a CSS class selector, that is used to select containers on the page, so we need the test to use a container property that is a string selector.
Right now you are trying to make the container property an object, which is totally and bloody useless.
Your insistence on trying to do the wrong thing, is only making it take more time before things can be done right.
My replies to you are only when I stop to get a cuppa tea, which is only about 4 times per day if we’re lucky. Right now most of them seem to be wasted because I must tell you that you are doing things wrong. I recommend that you waste as few of those as possible, so that beneficial progress can be made instead.