Console messages - Firefox Developer Tools 编辑

Most of the Web Console is occupied by the message display pane:

Each message is displayed as a separate row:

By default, the console is cleared each time you navigate to a new page or reload the current page. To override this behavior, enable Persist Logs in the console settings menu (gear icon).

The context menu options listed below are available on all message categories. Additional context menu options are described in the subsection for the message category they apply to.

• Copy Message copies the selected message to the clipboard.
• Select All selects all messages available in the message display pane.
• Export Visible Messages To
  • Clipboard copies all messages available in the display pane to the clipboard.
  • File opens a file dialog box so you can save an export of all messages available in the display pane.

Message categories

Network

Network log messages are not shown by default. Use the filtering feature to show them.

Network requests are logged with a line that looks like this:

The context menu for network messages includes a few extra items in addition the globally-available ones:

Copy link location

Acts as you would expect, copying the URL into the clipboard

Open in Network Panel

Switches context to the Network tab, selects the request and shows you the details

Resend Request

Sends the network request again.

Open URL in New Tab

Opens the URL in a new browser tab. If the resource is an image, the image will be opened in a new tab. If the resource is a stylesheet, you will see the CSS rules, etc.

JS

JavaScript errors contain a "Learn more" link that takes you to the JavaScript error reference containing additional advice for fixing issues:

Source maps

The Web Console understands source maps. This means that if your JavaScript sources are compressed, you can supply a source map for them. Then any messages or errors your source generates will show up in the Web Console with a link back to the original source, not the compressed version.

Async stack frames

Stack traces show stack frames for async functions separately from those for synchronous functions. When you run code containing an async function, its traces (console.trace or thrown error) are shown with an Async: prefix.

CSS

Note: CSS warnings and reflow messages are not shown by default, for performance reasons (see bug 1452143). Use the filtering feature to show them.

Some CSS messages contain a disclosure triangle at the left of the message. Click it to view more information about the error, as well as which DOM nodes are affected by the error.

Security

The security messages shown in the Web Console help developers find potential or actual vulnerabilities in their sites. Additionally, many of these messages help educate developers because they end with a “Learn More” link that takes you to a page with background information and advice for mitigating the issue.

The complete list of security messages is as follows:

Bug 863874 is the meta-bug for logging relevant security messages to the Web Console. If you have more ideas for useful features like the ones discussed here, or are interested in contributing, check out the metabug and its dependencies.

Logging

Messages logged from Shared Workers, Service Workers, add-ons, and Chrome Workers are not shown by default. Use the filtering feature to show them.

The Logging category includes messages logged using the Console API.

The Web console supports the following Console API messages:

• assert()
• clear()
• count()
• dir()
• dirxml()
• error()
• exception()
• group()
• groupEnd()
• info()
• log()
• table()
• time()
• timeEnd()
• trace()
• warn()

The console prints a stack trace for all error messages, like this:

function foo() {
  console.error("it explodes");
}

function bar() {
  foo();
}

function doStuff() {
 bar();
}

doStuff();

Server

Server-side log messages was introduced in Firefox 43, but removed in Firefox 56. You can install the Chrome Logger extension to (re)-enable the feature.

With the Chrome Logger extension, Web Console can display messages sent from the server. This enables you to use the Web Console to debug server-side code.

It uses the Chrome Logger protocol. Briefly, the way it works is:

• Your server-side code — Python, PHP, Node.js, etc. — includes a library that provides a console API.
• Your server-side code uses this API to log messages.
• The server-side library creates JSON objects from the messages and encodes them for transmission.
• The messages are transmitted to the client as a response header named X-ChromeLogger-Data.
• The Web Console decodes these headers and displays them.

To find a suitable library for your server code, see the Chrome Logger documentation.

Interpreter input/output

Commands sent to the browser using the Web Console's JavaScript interpreter, and the corresponding responses, are logged in the console messages.

For responses that contain objects or variables, the following context menu options are available:

Reveal in Inspector

Shows the selected DOM node in the Inspector pane.

Store as Global Variable

Creates a global variable (with a name like temp0, temp1, etc.) whose value is the selected object. The name of the variable appears as an input to the interpreter, and its value appears as a response.

Copy Object

Copies the selected object to the clipboard.

Filtering and searching

Filtering by category

You can use the toolbar along the top to constrain the results displayed.

To see only messages of particular categories, click the button labeled with that category (Errors, CSS, and so on).

For Errors and Warnings, when you turn off display of the category, a number appears next to the button text to indicate how many messages of that type are available. For example, "Warnings (25)".

Network requests with response codes in the 400-499 (client error) or 500-599 (server error) ranges are considered errors. Their display is controlled by the Errors button, not the Requests button.

Filtering by text

To see only messages that contain a specific string, type in the text box labeled "Filter output". For example, if you entered the string img into the text box, you would have a list something like this:

A small "x" icon appears at the right end of the text box when you have entered a string on which to filter the output. Click the "x" icon to clear the filter and show the entire list again.

You can negate a text search by prefixing it with the - character. For example, -img shows only items that do not contain the string img.

Filtering with Regular Expressions

You can also use a valid regular expression to filter the console output. For example, the following video shows the results when filtering on two simple regular expressions: /(cool|rad)/ and /(cool)/.

You can negate a regular expression search by prefixing it with the - character. For example, -/(cool|rad)/ shows only items that do not match the expression /(cool|rad)/.

Clearing the log

Finally, you can use the trashcan icon on the left to clear the contents of the console. When you clear the console, the console cache is also cleared. This prevents errors that have already been logged from reappearing when you reopen the console.