How do I constantly check if my if statement returns true or false

I am trying to constantly check for any update on the page. I want to influence the second object on the page by checking if the user clicks a button that makes first object display as a block

So user click button > first object displays block > the second object should move. how do I constantly check for any changes in Javascript?

I currently have this

const button = document.querySelector(".btn")
const firstObject = document.querySelector(".first-object")

btn.addEventListener("click", function(){
   if(firstObject.style.display === "none"){
      firstObject.style.display = "block"
    } else { 
      firstObject.style.display = "none"
    }
})

So this sets the ".first-object" div to block or hides it , Now I want my second div to get a margin-top of 50px when the ".first-object" is set to block and so I added this

    const secondObject= document.querySelector(".second-object")

    if (object.style.display = "block"){
        secondObject.style.marginTop = "50px";
    } else {
        secondObject.style.marginTop = "0";
    }

But this part doesnt constantly check if the other value returns true. How do I achieve this?

Sorry for my noobish question and thanks in advance!