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What's New In DevTools (Chrome 66)

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

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.

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.

The Initiator column shows that all of the requests were initiated by line 2 of requests.js.
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.
Blackboxing requests.js.
Figure 2. Blackboxing requests.js
After blackboxing requests.js, the Initiator column now shows more helpful results.
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.

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

Manually pretty-printing the contents of analytics.js via the 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.

Previewing HTML in the Preview tab.
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.

An example of styles defined within HTML
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.

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

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

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

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

Feedback

The best place to discuss any of the features or changes you see here is the google-chrome-developer-tools@googlegroups.com 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 83

Chrome 82

Chrome 82 was cancelled.

Chrome 81

Chrome 80

Chrome 79

Chrome 78

Chrome 77

Chrome 76

Chrome 75

Chrome 74

Chrome 73

Chrome 72

Chrome 71

Chrome 70

Chrome 68

Chrome 67

Chrome 66

Chrome 65

Chrome 64

Chrome 63

Chrome 62

Chrome 61

Chrome 60

Chrome 59