Use XHR/fetch Breakpoints!

By  on  

Web debugging tools are so incredibly excellent these days. I remember the days where they didn't exist and debugging was a total nightmare, even for the simplest of problems. A while back I introduced many of you to Logpoints, a way to output console.log messages without needing to change the source files. Another great breakpoint type is XHR/fetch breakpoints, allowing you to pause execution when an AJAX call is made. Let's look at XHR/fetch breakpoints!

To set an XHR/fetch breakpoint, open your browser's Developer Tools and click the Sources tab -- the same tab you open for other breakpoints. Under the XHR/fetch accordion item, click the big "+" button. You'll see an empty text input:

Within that text input, type a string that you'd like to break all XHR/fetch calls on. For example, if I wanted to break any time a fetch request was made, I would input davidwalsh.name:

In the case above, a XHR/fetch request breakpoint halts execution because a request is made to https://davidwalsh.name/url-canparse. You'll be able to step through and step into like you can with regular breakpoints, and you'll get a full Call Stack pane to see how execution got to a given point.

XHR/fetch breakpoints are another great way to debug your web app. The more reliant we are on dynamic websites with frequently changing content, debugging fetch calls is a must. Happy debugging!

Recent Features

  • By
    Animated 3D Flipping Menu with CSS

    CSS animations aren't just for basic fades or sliding elements anymore -- CSS animations are capable of much more.  I've showed you how you can create an exploding logo (applied with JavaScript, but all animation is CSS), an animated Photo Stack, a sweet...

  • By
    fetch API

    One of the worst kept secrets about AJAX on the web is that the underlying API for it, XMLHttpRequest, wasn't really made for what we've been using it for.  We've done well to create elegant APIs around XHR but we know we can do better.  Our effort to...

Incredible Demos

Discussion

  1. // Function to make an XHR request to a fake API
    function makeXHRRequest() {
      const xhr = new XMLHttpRequest();
      xhr.open('GET', 'https://jsonplaceholder.typicode.com/posts/1', true);
    
      // Set a breakpoint here to inspect xhr object
      // debugger;
    
      xhr.onload = function () {
        if (xhr.status === 200) {
          const response = JSON.parse(xhr.responseText);
          console.log('XHR Response:', response);
    
          // Set a breakpoint here to inspect the response
          // debugger;
        } else {
          console.error('XHR Request failed with status:', xhr.status);
        }
      };
    
      xhr.send();
    }
    
    // Function to make a fetch request to a fake API
    async function makeFetchRequest() {
      // Set a breakpoint here to inspect fetch options
      // debugger;
    
      try {
        const response = await fetch('https://jsonplaceholder.typicode.com/posts/2');
        if (!response.ok) {
          throw new Error(Fetch Request failed with status: ${response.status});
        }
    
        const data = await response.json();
        console.log('Fetch Response:', data);
    
        // Set a breakpoint here to inspect the data
        // debugger;
      } catch (error) {
        console.error('Fetch Request Error:', error);
      }
    }
    
    // Call the XHR and Fetch functions
    makeXHRRequest();
    makeFetchRequest();
    

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!