CODE EXAMPLE FOR JAVASCRIPT

foreach function into arrow with addeventlistener

const toggleElements = document.querySelectorAll('.toggle');
toggleElements.forEach(el => {
  el.addEventListener('click', () => {
    this.classList.toggle('active'); // `this` refers to `window`
    // Error: Cannot read property 'toggle' of undefined
  });
});
This code will throw an error anytime the matching element is clicked, firing the event listener and executing the callback, due to the window object not having a classList property. Oftentimes, however, the code could fail silently as it might for example check for a condition that always evaluates to false for window while it should evaluate to true for a given element, resulting in many headaches and wasted hours until the issue is discovered and fixed.

To deal with this, one could simply use the first argument of the callback function and Event.target or Event.currentTarget depending on their needs:

const toggleElements = document.querySelectorAll('.toggle');
toggleElements.forEach(el => {
  el.addEventListener('click', (e) => {
    e.currentTarget.classList.toggle('active'); // works correctly
  });
});