What's New In DevTools (Chrome 66)

Published on Monday, February 26, 2018

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

Ignore script 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.

Ignore script 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.

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

Hover over the Initiator column. The call stack that caused the request appears in a pop-up.
Right-click the call that you want to hide from the initiator results.
Select Add script to ignore list. The Initiator column now hides any calls from the script that you ignored.

Figure 1. Ignoring requests.js

Manage your ignored scripts from the Ignore List tab in Settings.

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

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 2. 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 3. 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 4. 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 5. 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

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: Ignore 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 6. The click breakpoint pauses in Vue.js' wrapper code

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

Figure 7. Ignoring 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 8. The click breakpoint now pauses on the app's listener code

Download the preview channels

Consider using the Chrome Canary, Dev or Beta as your default development browser. These preview channels give you access to the latest DevTools features, test cutting-edge web platform APIs, and find issues on your site before your users do!

Getting in touch with the Chrome DevTools team

Use the following options to discuss the new features and changes in the post, or anything else related to DevTools.

Submit a suggestion or feedback to us via crbug.com.
Report a DevTools issue using the More options > Help > Report a DevTools issues in DevTools.
Tweet at @ChromeDevTools.
Leave comments on our What's new in DevTools YouTube videos or DevTools Tips YouTube videos.