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

Incredible Demos

  • By
    Drag & Drop Elements to the Trash with MooTools 1.2

    Everyone loves dragging garbage files from their desktop into their trash can. There's a certain amount of irony in doing something on your computer that you also do in real life. It's also a quick way to get rid of things. That's...

  • By
    “Top” Watermark Using MooTools

    Whenever you have a long page worth of content, you generally want to add a "top" anchor link at the bottom of the page so that your user doesn't have to scroll forever to get to the top. The only problem with this method is...

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!