Passing parameters to a module via closures in JavaScript

It is considered good practice not to hardcode any values into the module, but to pass them as a parameter of the module itself (that is, as a parameter of the function called in-place):

javascript;(function(arg1, arg2) { // the parameters get into variables
  
})(1, 2); // passing some parameters

Let's look at an example. Let's have a div with a number and a button:

html<div id="div">3</div>
<button id="btn">click me</button>

Suppose we also have some module:

javascript;(function() {
  let div = document.querySelector('#div');
  let btn = document.querySelector('#btn');
  
  function func(num) {
    return num * num;
  }
  
  btn.addEventListener('click', function() {
    div.textContent = func(div.textContent);
  });
})();

As you can see, our element selectors are hardcoded in the module code. A better solution would be to pass them as module parameters - so in the future we can easily change them. Let's refactor our module:

javascript;(function(selector1, selector2) {
  let div = document.querySelector(selector1);
  let btn = document.querySelector(selector2);
  
  function func(num) {
    return num * num;
  }
  
  btn.addEventListener('click', function() {
    div.textContent = func(div.textContent);
  });
})('#div', '#btn');