Mark Conroy's blog post titled "How to use once() in Drupal" provides practical insights into the application of the 'once()' library in Drupal. These insights are shared through a concise and compelling code snippet.

Once, a Drupal library—available on npm—ensures your JavaScript only runs once when working on any item. The provided code snippet is a valuable guide for developers aiming to ensure the precise execution of their JavaScript code for a designated item.

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Mark adopts a pragmatic approach by assigning the result of 'once()' to the variable 'editFrequencys,' always obtaining an array, even when dealing with a single item. This approach minimizes potential issues in case additional instances of the targeted element emerge on the webpage in the future.

const editFrequencys = once('allEditFrequencies', '.edit-frequency', context);

editFrequencys.forEach(editFrequency => {
  editFrequency.on('change', function() {
    $.ajax({
      method: "POST",
      url: "/frequency-select",
      data: { name: "John", location: "Boston" },
      dataType: "json"
    })
      .done(function( data ) {
        console.log("It's done!");
        console.log(data);
      });
  });
});

Within the presented example, the arguments in the first line fulfill distinct roles in the process. The label 'allEditFrequencies' acts as a distinctive identifier, linking the targeted DOM element to the 'once()' function. This label is then associated with a data attribute in the DOM, enabling the seamless identification of the specified item's relevant 'once()' function.

The inclusion of 'context' as a parameter in the code signifies the method used to locate the array of elements, with a preference for this over 'document' in Drupal to accommodate dynamic updates, particularly in scenarios involving AJAX.

Mark's practical explanation demystifies the usage of 'once().' It underscores the significance of future-proofing code by working with arrays, a prudent choice even when anticipating a solitary item on the webpage. Read more here.