Passing a callback to work with the DOM in JavaScript

Suppose we have some group of DOM elements:

html<p class="elem">1</p>
<p class="elem">2</p>
<p class="elem">3</p>
<p class="elem">4</p>
<p class="elem">5</p>

Let's make the function forEach, which will take the elements group selector as the first parameter, and the second parameter - a callback function , which will be applied to each of the found elements in turn:

javascriptforEach('.elem', function() {
  // the function will be applied to each element
});

Let the elements that fall under the selector, in turn, fall into the first parameter of the callback:

javascriptforEach('.elem', function(elem) {
  console.log(elem); // outputs the found elements one by one
});

Let's use our function to find all elements with the class elem and apply a callback for each element found, which will square the text of each element:

javascriptforEach('.elem', function(elem) {
  elem.textContent = elem.textContent ** 2;
});

Let's now write the implementation of the forEach function:

javascriptfunction forEach(selector, func) {
  let elems = document.querySelectorAll(selector);
  
  for (let elem of elems) {
    func(elem);
  }
}