What's New In DevTools (Chrome 66)

By Kayce Basques

Technical Writer, Chrome DevTools & Lighthouse

New features and major changes coming to DevTools in Chrome 66 include:

• Blackboxing in the Network panel
• Auto-adjust zooming in Device Mode
• Pretty-printing in the Preview and Response tabs
• Previewing HTML content in the Preview tab
• Local Overrides with styles inside of HTML

Note: Check what version of Chrome you're running at chrome://version. If you're running an earlier version, these features won't exist. If you're running a later version, these features may have changed. Chrome auto-updates to a new major version about every 6 weeks.

Read on, or watch the video version of the release notes below.

Blackboxing in the Network panel

The Initiator column in the Network panel tells you why a resource was requested. For example, if JavaScript causes an image to be fetched, the Initiator column shows you the line of JavaScript code that caused the request.

Note: You can hide or show columns in the Network panel by right-clicking the table header.

Previously, if your framework wrapped network requests in a wrapper, the Initiator column wouldn't be that helpful. All network requests pointed to the same line of wrapper code.

Figure 1. The Initiator column shows that all of the requests were initiated by line 2 of requests.js

What you really want in this scenario is to see the application code that causes the request. That's now possible:

1. Hover over the Initiator column. The call stack that caused the request appears in a pop-up.
2. Right-click the call that you want to hide from the initiator results.
3. Select Blackbox script. The Initiator column now hides any calls from the script that you blackboxed.

Figure 2. Blackboxing requests.js

Figure 3. After blackboxing requests.js, the Initiator column now shows more helpful results

Manage your blackboxed scripts from the Blackboxing tab in Settings.

See Ignore a script or pattern of scripts to learn more about blackboxing.

Pretty-printing in the Preview and Response tabs

The Preview tab in the Network panel now pretty-prints resources by default when it detects that those resources have been minified.

Figure 4. The Preview tab pretty-printing the contents of analytics.js by default

To view the unminified version of a resource, use the Response tab. You can also manually pretty-print resources from the Response tab, via the new Format button.

Figure 5. Manually pretty-printing the contents of analytics.js via the Format button

Previewing HTML content in the Preview tab

Previously, the Preview tab in the Network panel showed the code of an HTML resource in certain situations, while rendering a preview of the HTML in others. The Preview tab now always does a basic rendering of the HTML. It's not intended to be a full browser, so it may not display HTML exactly as you expect. If you want to see the HTML code, click the Response tab, or right-click a resource and select Open in Sources panel.

Figure 6. Previewing HTML in the Preview tab

Auto-adjust zooming in Device Mode

When in Device Mode, open the Zoom dropdown and select Auto-adjust zoom to automatically resize the viewport whenever you change device orientation.

Local Overrides now works with some styles defined in HTML

Back when DevTools launched Local Overrides in Chrome 65, one limitation was that it couldn't track changes to styles defined within HTML. For example, in Figure 7 there's a style rule in the head of the document that declares font-weight: bold for h1 elements.

Figure 7. An example of styles defined within HTML

In Chrome 65, if you changed the font-weight declaration via the DevTools Style pane, Local Overrides wouldn't track the change. In other words, on the next reload, the style would revert back to font-weight: bold. But in Chrome 66, changes like this now persist across page loads.

Caution: Local Overrides can track changes like this so long as the style is defined in the HTML document that was sent over the network. If you have a script that dynamically adds styles to an HTML document, Local Overrides still won't be able to detect those changes.

Bonus tip: Blackbox framework scripts to make Event Listener Breakpoints more useful

Note: This section is not related to Chrome 66. It's just a bonus tip about an existing feature that you may find useful.

Back when I created the Get Started With Debugging JavaScript video, some viewers commented that event listener breakpoints aren't useful for apps built on top of frameworks, because the event listeners are often wrapped in framework code. For example, in Figure 8 I've set up a click breakpoint in DevTools. When I click the button in the demo, DevTools automatically pauses in the first line of listener code. In this case, it pauses in Vue.js's wrapper code on line 1802, which isn't that helpful.

Figure 8. The click breakpoint pauses in Vue.js' wrapper code

Since the Vue.js script is in a separate file, I can blackbox that script from the Call Stack pane in order to make this click breakpoint more useful.

Figure 9. Blackboxing the Vue.js script from the Call Stack pane

The next time I click the button and trigger the click breakpoint, it executes the Vue.js code without pausing in it, and then pauses on the first line of code in my app's listener, which is where I really wanted to pause all along.

Figure 10. The click breakpoint now pauses on the app's listener code

A request from the DevTools team: consider Canary

If you're on Mac or Windows, please consider using Chrome Canary as your default development browser. If you report a bug or a change that you don't like while it's still in Canary, the DevTools team can address your feedback significantly faster.

Note: Canary is the bleeding-edge version of Chrome. It's released as soon as its built, without testing. This means that Canary breaks from time-to-time, about once-a-month, and it's usually fixed within a day. You can go back to using Chrome Stable while Canary is broken.

Feedback

The best place to discuss any of the features or changes you see here is the [e-mail] mailing list. You can also tweet us at @ChromeDevTools if you're short on time. If you're sure that you've encountered a bug in DevTools, please open an issue.

Discover other DevTools features

Below is a list of everything that's been covered in the What's New In DevTools series.

Chrome 72

• Visualize performance metrics in the Performance panel.
• Highlight text nodes in the DOM Tree.
• Copy the JS path to a DOM node.
• Audits panel updates, including a new audit that detects JS libraries and new keywords for accessing the Audits panel from the Command Menu.

Chrome 71

• Hover over a Live Expression result to highlight a DOM node.
• Store DOM nodes as global variables.
• Initiator and priority information now in HAR imports and exports.
• Access the Command Menu from the Main Menu.
• Picture-in-Picture breakpoints.

Chrome 70

• Live Expressions in the Console.
• Highlight DOM nodes during Eager Evaluation.
• Performance panel optimizations.
• More reliable debugging.
• Enable network throttling from the Command Menu.
• Autocomplete Conditional Breakpoints.
• Break on AudioContext events.
• Debug Node.js apps with ndb.
• (Bonus Tip) Measure real world user interactions with the User Timing API.

Chrome 68

• Eager Evaluation.
• Argument hints.
• Function autocompletion.
• ES2017 keywords.
• Lighthouse 3.0 in the Audits panel.
• BigInt support.
• Adding property paths to the Watch pane.
• "Show timestamps" moved to Settings.

Chrome 67

• Search across all network headers.
• CSS variable value previews.
• Copy as fetch.
• New audits, desktop configuration options, and viewing traces.
• Stop infinite loops.
• User Timing in the Performance tabs.
• JavaScript VM instances clearly listed in the Memory panel.
• Network tab renamed to Page tab.
• Dark theme updates.
• Certificate transparency information in the Security panel.
• Site isolation features in the Performance panel.

Chrome 66

• Blackboxing in the Network panel.
• Auto-adjust zooming in Device Mode.
• Pretty-printing in the Preview and Response tabs.
• Previewing HTML content in the Preview tab.
• Local Overrides support for styles inside of HTML.
• (Bonus Tip) Blackbox framework scripts to make Event Listener Breakpoints more useful.

Chrome 65

• Local Overrides.
• New accessibility tools.
• The Changes tab.
• New SEO and performance audits.
• Multiple recordings in the Performance panel.
• Reliable code stepping with workers in async code.

Chrome 64

• Performance Monitor.
• Console Sidebar.
• Group similar Console messages.

Chrome 63

• Multi-client remote debugging support.
• Workspaces 2.0.
• 4 new audits.
• Simulate push notifications with custom data.
• Trigger background sync events with custom tags.

Chrome 62

• Top-level await in the Console.
• New screenshot workflows.
• CSS Grid highlighting.
• A new Console API for querying objects.
• New Console filters.
• HAR imports in the Network panel.
• Previewable cache resources.
• More predictable cache debugging.
• Block-level code coverage.

Chrome 61

• Mobile device throttling simulation.
• View storage usage.
• View when a service worker cached responses.
• Enable the FPS meter from the Command Menu.
• Set mousewheel behavior to zoom or scroll.
• Debugging support for ES6 modules.

Chrome 60

• New Audits panel.
• 3rd-Party Badges.
• A new gesture for Continue To Here.
• Step into async.
• More informative object previews in the Console.
• More informative context selection in the Console.
• Real-time updates in the Coverage tab.
• Simpler network throttling options.
• Async stacks on by default.

Chrome 59

• CSS and JS code coverage.
• Full-page screenshots.
• Block requests.
• Step over async await.
• Unified Command Menu.