Chrome DevTools - Things You Should Know about Console

Preface

The Chrome DevTools includes a built-in tool for interacting with the JavaScript engine – which is the Console.
In order to master the Console – we should know its supported capabilities as much as possible.

Accordingly, we’re going to reveal several tips regarding the Console.

Opening the Console

To open the Console as a panel – press on CTRL+SHIFT+J (Windows/Linux) or CMD + OPT + J (Mac):

To open the Console as a drawer – press on CTRL + ` (Backtick):

Selecting Elements

We can execute querySelectorAll for selecting all elements by a selector using $$(selector):

Note: If we want to execute querySelector, we should use $(selector).

Last Evaluated Expression

To access the last evaluated expression, we can use $_:

Note: We can apply the appropriate methods on that expression, for instance – if it’s a DOM element, we’re able to invoke innerHTML and print the result into the Console.

Last Five Elements

In case that we traverse the DOM manually, we’ve the ability to access the last five watched elements. In order to do that, we can use the commands: $0, $1, $2, $3 and $4. $0 returns the current selected element whereas $1–$4 return the last historical elements respectively:

Copy to Clipboard

Sometimes we need to copy the string representation of an object to the clipboard:

Note: In previous versions of DevTools, we should have used copy(JSON.stringify(object)) in order to convert the JSON to a string. However, it isn’t needed anymore.

Registered Event Listeners

Printing the registered event listeners for an object is pretty easy because of getEventListeners(object):

Note: Assuming there is a button with click event in the page.

Monitoring a Function

We can track invocations for a function with the passed arguments using monitor(function):

Note: To stop the tracking – use unmonitor(function).

Monitoring an Events

We can track an events of an object using monitorEvents(object, [events]). The first argument is the actual specified object whereas the second is the specified array of events (or a single event).

Let’s listen and simulate clicks on the Window object:

A few points:

• To stop the tracking – use unmonitorEvents(object, [events]).
• We could use unmonitorEvents(object) to eliminate the tracking for all events.

Measuring Time

Measuring time for a dedicated action could be performed simply when invoking console.time(text) before the action and console.timeEnd(text) thereafter:

Styling Console Output

Applying CSS on the output text is performed using the %c string, which indicates the beginning of the styled text. The second parameter is a string of the specified CSS properties.

Here’s an example:

Hiding Network Messages

Network messages may appear in the Console in case of an error of a resource, blocking scripts and so on. From time to time, we don’t care about these messages and we wish to hide them:

Editing an Element

We can edit the content of an element directly through the Console:

Note: The element could be edited as HTML as well.

References

Check out the following links for more information:

• Console API
• Command Line API