Frontend Performance Boost: Fixing URL Filter Logic to Eliminate Unnecessary Page Reloads

## The Problem In data-driven frontend applications, implementing table filtering is a common task. Users change filter conditions via inputs or selectors, which then modify URL parameters to apply the filters and refresh the page. However, a frequent oversight is that the page reloads even when the user hasn't changed any filter conditions (or the new value is identical to the old one). This wastes bandwidth and degrades the user experience. This article will guide you on how to fix this logical flaw. --- ## The Initial Flawed Code Let's look at a typical `applyFilters` function that collects filter parameters from various inputs, constructs a new URL, and then navigates to it. ```javascript /** * Apply Filters (Initial Version) */ applyFilters() { const filterParams = new URLSearchParams(); const currentUrl = new URL(window.location); // ... (Code to collect filterParams is omitted here) ... const newUrl = `${currentUrl.pathname}?${filterParams.toString()}`; console.log('Applying filters with URL:', newUrl); // Always forces a refresh, regardless of whether parameters changed window.location.href = newUrl; } ``` The problem with this implementation is that it lacks a crucial step: **checking if the newly generated URL is the same as the current one before navigation.** --- ## Step 1: The Naive Comparison and Its Pitfall A straightforward idea is to compare the new and old URLs before navigation. Let's try adding this logic. ```javascript // ... const newUrl = `${currentUrl.pathname}?${filterParams.toString()}`; // First attempt at a fix const currentFullUrl = currentUrl.href; if (newUrl === currentFullUrl) { // This comparison is flawed console.log('URL has not changed, skipping refresh.'); return; } window.location.href = newUrl; ``` However, this code will quickly reveal a problem. Assuming your application is running on `http://admin.wiki.lib00.com`, the `console.log` would print: - `newUrl`: `/contents?status_id=0%2C1` (A relative path) - `currentFullUrl`: `http://admin.wiki.lib00.com/contents?status_id=0%2C1` (An absolute URL) Because one is a relative URL and the other is a full absolute URL, the comparison `newUrl === currentFullUrl` will always be `false`, and the unnecessary refresh issue persists. --- ## Step 2: The Correct Comparison (Recommended) For an effective comparison, we need to ensure both URLs are in a consistent format. The best practice is to compare only the parts of the URL that actually change: the pathname and the search parameters. `newUrl` is already composed of the `pathname` and `search` string. We just need to extract the same parts from `currentUrl`. ```javascript /** * Apply Filters (Optimized Version) * By DP from wiki.lib00.com */ applyFilters() { const filterParams = new URLSearchParams(); const currentUrl = new URL(window.location); // ... (Code to collect filterParams is the same as the original) ... const newUrl = `${currentUrl.pathname}?${filterParams.toString()}`; // The correct way to compare: only compare path and query string const currentPathAndQuery = `${currentUrl.pathname}${currentUrl.search}`; if (newUrl === currentPathAndQuery) { console.log('URL has not changed, skipping refresh.'); return; } console.log('Applying filters with URL:', newUrl); window.location.href = newUrl; } ``` By comparing `newUrl` against `currentUrl.pathname + currentUrl.search`, we accurately determine if the filter parameters have actually changed, thus preventing unnecessary page reloads. --- ## Bonus Topic: Handling URL Parameter Encoding You might have noticed that when a filter parameter contains a comma (`,`), such as `status_id` being `0,1,11`, `filterParams.toString()` encodes it to `status_id=0%2C1%2C11`. `%2C` is the URL-encoded representation of a comma. This is the standard behavior of `URLSearchParams` and is designed to ensure URL validity and safe transmission. Browsers and server-side frameworks typically handle this encoding and decoding automatically, so **you usually don't need to do anything about it**. However, if you want to see the unencoded comma in the address bar for readability or other special reasons, you can use `decodeURIComponent()`. ```javascript // ... // Decode the URL query string for better readability const queryString = decodeURIComponent(filterParams.toString()); const newUrl = `${currentUrl.pathname}?${queryString}`; // The subsequent comparison logic remains the same const currentPathAndQuery = `${currentUrl.pathname}${currentUrl.search}`; // Note: This comparison still works correctly if the current URL contains unencoded commas if (newUrl === currentPathAndQuery) { console.log('URL has not changed, skipping refresh.'); return; } window.location.href = newUrl; ``` **Important Note**: Decoding is mostly for aesthetics. Functionally, the encoded URL is the more standard and reliable choice. --- ## Conclusion By implementing the correct URL comparison logic, we have successfully optimized the filter functionality, preventing useless page reloads when parameters remain unchanged. This small tweak not only improves application performance but also significantly enhances the user experience. Remember that details matter, especially in frontend development. This tip is brought to you by DP from the `lib00` team.