path: root/files/es/tools/web_console/index.html

---
title: Consola Web
slug: Tools/Web_Console
tags:
  - Debugging
  - Guide
  - NeedsTranslation
  - Security
  - Tools
  - TopicStub
  - Web Development
  - 'Web Development:Tools'
  - web console
translation_of: Tools/Web_Console
---
<p>La Consola Web:</p>

<ol>
 <li>Muestra la informacion asociada con los Logs de la pagina Web: cualquier solicitud de red, JavaScript, CSS, y errores de seguridad y advertencias, asi como tambien, advertencias, mensajes informativos explicitamente generados por Javascripten tiempo de ejecucion dentro del contexto de la pagina.</li>
 <li>te permite interactuar con la pagina ejecutando expresiones Javascript en el contexto de la página.</li>
</ol>

<p>It's part of the replacement for the old <a href="/en/Error_Console" title="en/Error Console">Error Console</a> built into Firefox: but the Error Console showed errors, warnings, and messages from all web pages, from the browser's own code, and from add-ons. This makes it much more difficult to see which messages are relevant to a specific page. The Web Console is always associated with a specific web page and only shows information associated with that page.</p>

<p>The other half of the replacement for the Error console is the <a href="/en-US/docs/Tools/Browser_Console" title="/en-US/docs/Tools/Browser_Console">Browser Console</a>, which shows errors, warnings, and messages from the browser's code and from add-ons.</p>

<p>{{EmbedYouTube("C6Cyrpkb25k")}}</p>

<h2 id="Abriendo_la_Consola_WEB">Abriendo la Consola WEB</h2>

<p>To open the Web Console select "Web Console" from the Web Developer submenu in the Firefox Menu (or Tools menu if you display the menu bar or are on Mac OS X), or by pressing its Control-Shift-K (Command-Option-K on the Mac) keyboard shortcut.</p>

<p>The <a href="https://developer.mozilla.org/en-US/docs/Tools/DevTools_Window" title="/en-US/docs/Tools/DevTools_Window">Toolbox</a> will appear at the bottom of the browser window, with the Web Console activated (it's just called "Console" in the <a href="/en-US/docs/Tools/DevTools_Window#Toolbar" title="/en-US/docs/Tools/DevTools_Window#Toolbar">DevTools toolbar</a>):</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/5581/web-console.png" style="display: block; margin-left: auto; margin-right: auto;"></p>

<p>Underneath the <a href="/en-US/docs/Tools/DevTools_Window#Toolbar" title="/en-US/docs/Tools/DevTools_Window#Toolbar">DevTools Window's own toolbar</a>, the Web Console's interface is split into three sections:</p>

<ul>
 <li><a href="#filtering-and-searching" title="#filtering-and-searching">Toolbar</a>: along the top is a toolbar containing buttons with labels like "Net", "CSS", and "JS". This toolbar is used to filter which messages are displayed</li>
 <li><a href="#command-line" title="#command-line">Command Line</a>: along the bottom is a command line that you can use to enter JavaScript expressions</li>
 <li><a href="#message-display-pane" title="#message-display-pane">Message Display Pane</a>: in between the toolbar and the command line, and occupying most of the window, is the space in which the Web Console displays messages</li>
</ul>

<h2 id="Message_Display_Pane"><a name="message-display-pane">Message Display Pane</a></h2>

<p>Most of the Web Console is occupied by the message display pane:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/5599/web-console-messages-highlighted.png" style="display: block; margin-left: auto; margin-right: auto;"></p>

<p>The message display pane displays the following sorts of messages:</p>

<ul>
 <li>HTTP requests</li>
 <li>Warnings and errors (including JavaScript, CSS, security warnings and errors, and messages explicitly logged by JavaScript code using the <a href="/en-US/docs/Web/API/console" title="/en-US/docs/Web/API/console">console</a> API)</li>
 <li>Input/output messages: commands send to the browser via the Web Console's command line, and the result of executing them.</li>
</ul>

<p>Each message is displayed as a single row in the pane.</p>

<h3 id="HTTP_requests">HTTP requests</h3>

<p>HTTP requests are logged with a line that looks like this:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/5593/web-console-message-request-annotated.png" style="display: block; margin-left: auto; margin-right: auto;"></p>

<ul>
 <li><strong>Time</strong>: the time the message was recorded</li>
 <li><strong>Category</strong>: this indicates that the message is an HTTP request</li>
 <li><strong>Method</strong>: the specific HTTP request method</li>
 <li><strong>URI</strong>: the target URI</li>
 <li><strong>Summary</strong>: the HTTP version, status code, and time taken to complete</li>
</ul>

<p>By default, the Web Console does not log request and response bodies: to do this, activate the context menu in the Web Console and select "Log Request and Response Bodies".</p>

<p>If you click on the message, you'll see a window like this, containing more details about the request and response:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/3148/detailspanel.png" style="display: block; height: 502px; margin-left: auto; margin-right: auto; width: 430px;">Scrolling down reveals the response headers. By default, the Web Console does not log request and response bodies: to do this, activate the context menu in the Web Console and select "Log Request and Response Bodies", reload the page, and you'll then see them in the "Inspect Network Request" window.</p>

<p>Only the first megabyte of data is logged for each request or response body, so very large requests and responses will be truncated.</p>

<h3 id="Warnings_and_errors">Warnings and errors</h3>

<p>Warnings and errors are logged with a line looking something like this:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/5585/web-console-message-annotated.png" style="display: block; margin-left: auto; margin-right: auto;"></p>

<ul>
 <li><strong>Time</strong>: the time the message was recorded. From Firefox 28 onwards this is not shown by default, and you can opt to see timestamps using a <a href="/en-US/docs/Tools_Toolbox#Settings">setting in the Toolbox</a>.</li>
 <li><strong>Category</strong>: this indicates what sort of message this is:
  <ul style="margin-left: 40px;">
   <li><span style="color: #0099ff;"><strong>Blue</strong></span>: CSS warning/error</li>
   <li><strong><span style="color: #ff8c00;">Orange</span></strong>: JavaScript warning/error</li>
   <li><span style="color: #ff0000;"><strong>Red</strong></span>: security warning/error</li>
   <li><span style="color: #a9a9a9;"><strong>Light Gray</strong></span>: message explicitly logged from JavaScript code using the <a href="/en-US/docs/Web/API/console" title="/en-US/docs/Web/API/console">console</a> API</li>
  </ul>
 </li>
 <li><strong>Type</strong>: an icon indicating whether it is an error(☓) or a warning(⚠).</li>
 <li><strong>Message</strong>: the message itself</li>
 <li><strong>Number of occurrences</strong>: if a line that generates a warning or error is executed more than once, it is only logged once, and this counter appears to indicate how many times it was encountered.</li>
 <li><strong>Filename and line number</strong>: a link to the filename and line number that generated the message</li>
</ul>

<h4 id="Security_messages">Security messages</h4>

<p>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.</p>

<p>The complete list of security messages is as follows:</p>

<table class="standard-table" style="width: auto;">
 <tbody>
  <tr>
   <th scope="col">Message</th>
   <th scope="col">Details</th>
  </tr>
  <tr>
   <td>Blocked loading mixed active content</td>
   <td>The page contained mixed active content: that is, the main page was served over HTTPS, but asked the browser to load "active content", such as scripts, over HTTP. The browser blocked this active content. See <a href="/en-US/docs/Security/MixedContent">Mixed Content</a> for more details.</td>
  </tr>
  <tr>
   <td>Blocked loading mixed display content</td>
   <td>The page contained mixed display content: that is, the main page was served over HTTPS, but asked the browser to load "display content", such as images, over HTTP. The browser blocked this display content. See <a href="/en-US/docs/Security/MixedContent">Mixed Content</a> for more details.</td>
  </tr>
  <tr>
   <td>Loading mixed (insecure) active content on a secure page
    <div class="geckoVersionNote">
    <p>Introduced in Firefox 26</p>
    </div>
   </td>
   <td>The page contained mixed active content: that is, the main page was served over HTTPS, but asked the browser to load "active content", such as scripts, over HTTP. The browser loaded this active content. See <a href="/en-US/docs/Security/MixedContent">Mixed Content</a> for more details.</td>
  </tr>
  <tr>
   <td>Loading mixed (insecure) display content on a secure page
    <div class="geckoVersionNote">
    <p>Introduced in Firefox 26</p>
    </div>
   </td>
   <td>The page contained mixed display content: that is, the main page was served over HTTPS, but asked the browser to load "display content", such as images, over HTTP. The browser loaded this display content. See <a href="/en-US/docs/Security/MixedContent">Mixed Content</a> for more details.</td>
  </tr>
  <tr>
   <td>This site specified both an X-Content-Security-Policy/Report-Only header and a Content-Security-Policy/Report-Only header. The X-Content-Security-Policy/Report-Only header(s) will be ignored.</td>
   <td>See <a href="/en-US/docs/Security/CSP">Content Security Policy</a> for more details.</td>
  </tr>
  <tr>
   <td>The X-Content-Security-Policy and X-Content-Security-Report-Only headers will be deprecated in the future. Please use the Content-Security-Policy and Content-Security-Report-Only headers with CSP spec compliant syntax instead.</td>
   <td>See <a href="/en-US/docs/Security/CSP">Content Security Policy</a> for more details.</td>
  </tr>
  <tr>
   <td>Password fields present on an insecure (http://) page. This is a security risk that allows user login credentials to be stolen.
    <div class="geckoVersionNote">
    <p>Introduced in Firefox 26</p>
    </div>
   </td>
   <td>Pages containing login forms must be served over HTTPS, not HTTP.</td>
  </tr>
  <tr>
   <td>Password fields present in a form with an insecure (http://) form action. This is a security risk that allows user login credentials to be stolen.
    <div class="geckoVersionNote">
    <p>Introduced in Firefox 26</p>
    </div>
   </td>
   <td>Forms containing password fields must submit them over HTTPS, not HTTP.</td>
  </tr>
  <tr>
   <td>Password fields present on an insecure (http://) iframe. This is a security risk that allows user login credentials to be stolen.
    <div class="geckoVersionNote">
    <p>Introduced in Firefox 26</p>
    </div>
   </td>
   <td>iframes containing login forms must be served over HTTPS, not HTTP.</td>
  </tr>
  <tr>
   <td>The site specified an invalid Strict-Transport-Security header.</td>
   <td>See <a href="/en-US/docs/Security/HTTP_Strict_Transport_Security">HTTP Strict Transport Security</a> for more details.</td>
  </tr>
 </tbody>
</table>

<p><a href="https://bugzilla.mozilla.org/show_bug.cgi?id=863874">Bug 863874</a> 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.</p>

<h3 id="Reflow_events">Reflow events</h3>

<div class="geckoVersionNote">
<p>Reflow events are only logged from Firefox Desktop 27+ and Firefox OS 1.3+.</p>
</div>

<p>The Web Console also logs reflow events. A reflow is the name given to the operation in which the browser calculates the layout of all or part of the page. Reflows occur when a change has happened to a page that the browser thinks affects the layout. Many events can trigger reflows, including: resizing the browser window, activating pseudoclasses like <a href="/en-US/docs/Web/CSS/:hover">:hover</a>, or manipulating the DOM in JavaScript.</p>

<p>Because reflows can be computationally expensive and directly affect the user interface, they can have a big impact on the responsiveness of a website or web app. By logging reflow events the Web Console can give you insight into when reflow events are being triggered, how long they take to execute and, if the reflows are <a href="#synchronous-and-asynchronous-reflows">synchronous reflows</a> triggered from JavaScript, which code triggered them.</p>

<p>Reflow events are logged under the CSS category, as "Log" messages, as distinct from CSS errors or warnings. By default, they are disabled. You can enable them by clicking the "CSS" button in the <a href="#filtering-and-searching">toolbar</a> and selecting "Log".</p>

<p>Each message is labeled "reflow" and shows the time taken to execute the reflow:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/6365/web-console-reflow-asynch.png" style="display: block; height: 53px; margin-left: auto; margin-right: auto; width: 554px;">If the reflow is a synchronous reflow triggered from JavaScript, it also shows a link to the line of code that triggered the reflow:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/6367/web-console-reflow-synch.png" style="display: block; height: 51px; margin-left: auto; margin-right: auto; width: 554px;">Click the link to open the file in the <a href="/en-US/docs/Tools/Debugger">Debugger</a>.</p>

<h4 id="Synchronous_and_asynchronous_reflows"><a name="synchronous-and-asynchronous-reflows">Synchronous and asynchronous reflows</a></h4>

<p>If a change is made that invalidates the current layout - for example, the browser window is resized or some JavaScript modifies an element's CSS - the layout is not recalculated immediately. Instead, the reflow happens asynchronously, the next time the browser decides it needs to be done (generally, the next time the browser repaints). In this way the browser can save up a collection of invalidating changes and recalculate their effect at once.</p>

<p>However, if some JavaScript code reads a style that has been modified, then the browser must perform a synchronous reflow in order to calculate the computed style to return. For example, code like this will cause an immediate, synchronous, reflow, when it calls <code>window.getComputedStyle(thing).height</code>:</p>

<pre class="brush: js">var thing = document.getElementById("the-thing");
thing.style.display = "inline-block";
var thingHeight = window.getComputedStyle(thing).height;</pre>

<p>Because of this, it's a good idea to avoid interleaving write and read calls to an element's styles when manipulating the DOM, because every time you read back a style that has been invalidated by a previous write call, you force a synchronous reflow.</p>

<h3 id="Inputoutput_messages">Input/output messages</h3>

<p>Commands sent to the browser using the <a href="#command-line" title="#command-line">Web Console's command line</a>, and the corresponding responses, are logged using lines like this:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/5587/web-console-message-input-output.png" style="display: block; height: 68px; margin-left: auto; margin-right: auto; width: 554px;">The dark gray bar indicates that these are input/output messages, while the direction of the arrow discriminates between input and output.</p>

<h3 id="Filtering_and_searching"><a name="filtering-and-searching">Filtering and searching</a></h3>

<p>You can use the toolbar along the top to constrain the results displayed.</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/5601/web-console-toolbar-highlighted.png" style="display: block; margin-left: auto; margin-right: auto;">You can display only specific types of messages or only message containing specific strings.</p>

<p>Finally, you can use this toolbar to clear the log.</p>

<dl>
</dl>

<h2 id="The_command_line_interpreter"><a name="command-line">The command line interpreter</a></h2>

<p>You can interpret JavaScript expressions in real time using the command line provided by the Web Console.</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/5597/web-console-commandline-highlighted.png" style="display: block; margin-left: auto; margin-right: auto;"></p>

<h3 id="Basic_operation">Basic operation</h3>

<h4 id="Entering_expressions">Entering expressions</h4>

<p>To enter expressions just type into the command line and press "Enter". To enter multiline expressions, use "Shift+Enter" instead of "Enter".</p>

<p>The expression you type is echoed in the message display window, followed by the result:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/5615/web-console-commandline-simple.png" style="display: block; height: 92px; margin-left: auto; margin-right: auto; width: 632px;"></p>

<h4 id="Accessing_variables">Accessing variables</h4>

<p>You can access variables defined in the page, both built-in variables like <code>window</code> and variables added by JavaScript like <code>jQuery</code>:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/5609/web-console-commandline-href.png" style="display: block; height: 89px; margin-left: auto; margin-right: auto; width: 632px;"><img alt="" src="https://mdn.mozillademos.org/files/5611/web-console-commandline-jquery.png" style="display: block; height: 92px; margin-left: auto; margin-right: auto; width: 632px;"></p>

<h4 id="Autocomplete">Autocomplete</h4>

<p>The command line has autocomplete: enter the first few letters and a popup appears with possible completions:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/5607/web-console-commandline-autocomplete.png" style="display: block; height: 125px; margin-left: auto; margin-right: auto; width: 632px;">Type "Enter" or "Tab" to accept the suggestion, use the up/down arrows to move to a different suggestion, or just keep typing if you don't like any of the suggestions.</p>

<div class="geckoVersionNote">
<p>New in Firefox 28</p>
</div>

<p>Starting from Firefox 28, the console suggests completions from the scope of the currently executing stack frame. This means that if you've hit a breakpoint in a function you get autocomplete for objects local to the function.</p>

<h4 id="Inspecting_objects">Inspecting objects</h4>

<p>If the result object is an object it appears in square brackets and is underlined, like this: <code><u>[object Function]</u></code>. Click on it, and you'll see a new panel appear containing details of the object:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/5613/web-console-commandline-object-details.png" style="display: block; margin-left: auto; margin-right: auto;">To dismiss this panel press "Escape".</p>

<h4 id="Defining_variables">Defining variables</h4>

<p>You can define your own variables, and then access them:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/5605/web-console-commandline-addvariable.png" style="display: block; height: 125px; margin-left: auto; margin-right: auto; width: 632px;"><img alt="" src="https://mdn.mozillademos.org/files/5603/web-console-commandline-addfunction.png" style="display: block; height: 168px; margin-left: auto; margin-right: auto; width: 632px;"></p>

<h4 id="Command_history">Command history</h4>

<p>The command line remembers commands you've typed: to move back and forward through your history, use the up and down arrows.</p>

<h3 id="Keyboard_shortcuts">Keyboard shortcuts</h3>

<table class="standard-table" style="width: auto;">
 <tbody>
  <tr>
   <td class="header">Shortcut</td>
   <td class="header">Description</td>
  </tr>
  <tr>
   <td>↑</td>
   <td>Moves to the previous entry in the command history, or, if an autocomplete popup is open, highlights the previous suggestion.</td>
  </tr>
  <tr>
   <td>↓</td>
   <td>Moves to the next entry in the command history, or, if an autocomplete popup is open, highlights the next suggestion.</td>
  </tr>
  <tr>
   <td>Ctrl-A</td>
   <td>Moves the cursor to the beginning of the line. (Note: beginning with Firefox 22, this will select all text on Windows)</td>
  </tr>
  <tr>
   <td>Ctrl-E</td>
   <td>Moves the cursor to the end of the line.</td>
  </tr>
  <tr>
   <td>Return</td>
   <td>Executes the code typed on the command line, or, if an autocomplete popup is open, chooses the current suggestion.</td>
  </tr>
  <tr>
   <td>Shift-Return</td>
   <td>Expands the height of the text input box for the command line by a line.</td>
  </tr>
  <tr>
   <td>Escape</td>
   <td>Cancels the autocompletion popup.</td>
  </tr>
  <tr>
   <td>Tab</td>
   <td>Generates an autocomplete suggestion and accepts the first one.</td>
  </tr>
 </tbody>
</table>

<h3 id="Helper_commands">Helper commands</h3>

<p>{{ page("/en/Using_the_Web_Console/Helpers", "The commands") }}</p>

<h2 id="The_split_console">The split console</h2>

<div class="geckoVersionNote">
<p>The split console is new in Firefox 28.</p>
</div>

<p>{{EmbedYouTube("G2hyxhPHyXo")}}</p>

<p>Starting in Firefox 28, you can use the console alongside other tools. While you're in another tool in the Toolbox, just press "Escape" or press the "Toggle split console" button in the <a href="/en-US/docs/Tools_Toolbox#Toolbar">Toolbar</a>. The toolbox will now appear split, with the original tool above and the web console underneath.</p>

<p>As usual, <code>$0</code> works as a shorthand for the element currently selected in the Inspector:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/6619/web-console-split-inspector.png" style="display: block; margin-left: auto; margin-right: auto;">When you use the split console with the debugger, the console's scope is the currently executing stack frame. So if you hit a breakpoint in a function, the scope will be the function's scope. You'll get autocomplete for objects defined in the function, and can easily modify them on the fly:</p>

<p><img alt="" src="https://mdn.mozillademos.org/files/6621/web-console-split-debugger.png" style="display: block; margin-left: auto; margin-right: auto;"></p>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="/en/Tools/Web_Console/Helpers" title="en/Using the Web Console/Helpers">Web Console Helpers</a></li>
 <li>{{ domxref("console") }}</li>
</ul>

<p>{{ languages( { "ja": "ja/Tools/Web_Console"} ) }}</p>