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Implementing a pagination feature with promises

Pagination is a common feature in web applications where data needs to be displayed in smaller chunks rather than loading everything at once. With the advent of asynchronous programming, promises have become a popular choice for handling asynchronous operations in JavaScript. In this blog post, we will explore how to implement a pagination feature using promises.

Prerequisites

To follow along with this tutorial, you should have a basic understanding of JavaScript, as well as familiarity with promises. If you are new to promises, I recommend reading the MDN documentation to get started.

Scenario

Let’s consider a scenario where we have an API that allows us to fetch a list of items. We want to display these items in a paginated manner, fetching a few items at a time and dynamically loading more as the user scrolls.

Implementation Steps

  1. Create a function to fetch a page of items from the API. This function should return a promise that resolves with the fetched items. You can use the fetch API or any other library for making HTTP requests.
function fetchItems(pageNumber) {
  return new Promise((resolve, reject) => {
    // Make a request to the API with the specified page number
    fetch(`/api/items?page=${pageNumber}`)
      .then(response => response.json())
      .then(data => resolve(data))
      .catch(error => reject(error));
  });
}
  1. Create a function to handle the pagination logic. This function will be responsible for fetching and displaying the items.
function handlePagination() {
  let pageNumber = 1;

  function loadNextPage() {
    fetchItems(pageNumber)
      .then(items => {
        // Display the fetched items on the page
        items.forEach(item => {
          // Code to display an item on the page
        });

        // Increment the page number for the next fetch
        pageNumber++;

        // Check if there are more pages to fetch
        if (items.length > 0) {
          // If there are more items, listen for scroll event to trigger loading the next page
          window.addEventListener("scroll", handleScroll);
        } else {
          // If there are no more items, remove the scroll event listener
          window.removeEventListener("scroll", handleScroll);
        }
      })
      .catch(error => {
        console.error("Error fetching items:", error);
      });
  }

  function handleScroll() {
    // Code to check if the user has scrolled to the bottom of the page

    if (isBottomOfPage()) {
      // Unload the scroll event listener to prevent multiple requests
      window.removeEventListener("scroll", handleScroll);

      // Load the next page of items
      loadNextPage();
    }
  }

  // Start loading the first page of items
  loadNextPage();
}
  1. Call the handlePagination function to initialize the pagination feature.
handlePagination();

Summary

By implementing pagination with promises, we can easily load and display data in a more efficient and user-friendly manner. Promises provide a clean and concise way to handle asynchronous operations, allowing us to focus on the logic of fetching and displaying the data.

References

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