Add JavaScript code in React component and calling it

How to add JavaScript code that I copied from a website in React component and call it using onclick?

this is my code that I copied

function myFunction() {
  var hide = document.getElementsByClassName("hide");
  var btnText = document.getElementById("myBtn");

  if (hide.style.display === "none") {
    btnText.innerHTML = "Loadmore";
    hide.style.display = "none";
  } else {
    btnText.innerHTML = "Load less";
    hide.style.display = "block";
  }
}

I have created a component where I had created a button tag. I want to call the function using onclick. How do I do that?