D3 Pass an Object to .attr or .style

I have a D3 selection:

let container = d3.select("div#container")

I want to append an object to it's styling - this object is dynamic that is why I cannot just hardcode it.

Example object:

let obj = {'style':'background-color:red;'}

Eample changes to object

if(x > 1) {
   obj = {'style':'background-color:green;'}
} else if (x < 0) {
   obj = {'style':'background-color:yellow;'}
}

I want to do something similar to

container.attr(obj); // Unsure if it should be attr or not

However, I am unsure how to obtain this. Any suggestions?