Window.open()

The open() method of the Window interface loads a specified resource into a new or existing browsing context (that is, tab, window, or <iframe>) under a specified name.

url Optional

A string indicating the URL or path of the resource to be loaded. If an empty string ("") is specified or this parameter is omitted, a blank page is opened into the targeted browsing context.

target Optional

A string, without whitespace, specifying the name of the browsing context the resource is being loaded into. If the name doesn't identify an existing context, a new context is created and given the specified name. The special target keywords, _self, _blank, _parent, and _top, can also be used.

This name can be used as the target attribute of <a> or <form> elements.

windowFeatures Optional

A string containing a comma-separated list of window features in the form name=value — or for boolean features, just name. These features include options such as the window's default size and position, whether or not to open a minimal popup window, and so forth. The following options are supported:

popup

If this feature is enabled, it requests that a minimal popup window be used. The UI features included in the popup window will be automatically decided by the browser, generally including an address bar only.

If popup is not enabled, and there are no window features declared, the new browsing context will be a tab.

Note: Specifying any features in the windowFeatures parameter, other than noopener or noreferrer, also has the effect of requesting a popup.

To enable the feature, specify popup either with no value at all, or else set it to yes, 1, or true.

Example: popup=yes, popup=1, popup=true, and popup all have identical results.

Note: The true value was introduced in March 2022. For better compatibility with older browsers, use one of the other values.

width or innerWidth

Specifies the width of the content area, including scrollbars. The minimum required value is 100.

height or innerHeight

Specifies the height of the content area, including scrollbars. The minimum required value is 100.

left or screenX

Specifies the distance in pixels from the left side of the work area as defined by the user's operating system where the new window will be generated.

top or screenY

Specifies the distance in pixels from the top side of the work area as defined by the user's operating system where the new window will be generated.

noopener

If this feature is set, the new window will not have access to the originating window via Window.opener and returns null.

When noopener is used, non-empty target names, other than _top, _self, and _parent, are treated like _blank in terms of deciding whether to open a new browsing context.

noreferrer

If this feature is set, the browser will omit the Referer header, as well as set noopener to true. See rel="noreferrer" for more information.

A WindowProxy object. The returned reference can be used to access properties and methods of the new window as long as it complies with Same-origin policy security requirements.

The Window interface's open() method takes a URL as a parameter, and loads the resource it identifies into a new or existing tab or window. The target parameter determines which window or tab to load the resource into, and the windowFeatures parameter can be used to control the size and position of a new window, and to open the new window as a popup with minimal UI features.

Note that remote URLs won't load immediately. When window.open() returns, the window always contains about:blank. The actual fetching of the URL is deferred and starts after the current script block finishes executing. The window creation and the loading of the referenced resource are done asynchronously.

The following example demonstrates how to implement the popup feature.

let windowObjectReference;
let windowFeatures = "popup";

function openRequestedPopup() {
  windowObjectReference = window.open("http://www.mozilla.org/", "mozillaWindow", windowFeatures);
}

We can also control the size and position of the new window.

let windowObjectReference;
let windowFeatures = "left=100,top=100,width=320,height=320";

function openRequestedPopup() {
  windowObjectReference = window.open("http://www.mozilla.org/", "mozillaWindow", windowFeatures);
}

Alternatively, we can open a new tab by omitting window features.

let windowObjectReference;

function openRequestedPopup() {
  windowObjectReference = window.open("http://www.mozilla.org/", "mozillaTab");
}

<script type="text/javascript">
var windowObjectReference = null; // global variable
function openFFPromotionPopup() {
  if(windowObjectReference == null || windowObjectReference.closed)
  /* if the pointer to the window object in memory does not exist
     or if such pointer exists but the window was closed */
  {
    windowObjectReference = window.open("http://www.spreadfirefox.com/",
   "PromoteFirefoxWindowName", "popup");
    /* then create it. The new window will be created and
       will be brought on top of any other window. */
  }
  else
  {
    windowObjectReference.focus();
    /* else the window reference must exist and the window
       is not closed; therefore, we can bring it back on top of any other
       window with the focus() method. There would be no need to re-create
       the window or to reload the referenced resource. */
  };
}
</script>
(...)
<p><a
 href="http://www.spreadfirefox.com/"
 target="PromoteFirefoxWindowName"
 onclick="openFFPromotionPopup(); return false;"
 title="This link will create a new window or will re-use an already opened one"
>Promote Firefox adoption</a></p>

The above code solves a few usability problems related to links opening secondary window. The purpose of the return false in the code is to cancel default action of the link: if the onclick event handler is executed, then there is no need to execute the default action of the link. But if JavaScript support is disabled or non-existent on the user's browser, then the onclick event handler is ignored and the browser loads the referenced resource in the target frame or window that has the name "PromoteFirefoxWindowName". If no frame nor window has the name "PromoteFirefoxWindowName", then the browser will create a new window and will name it "PromoteFirefoxWindowName".

More reading on the use of the target attribute:

HTML 4.01 Target attribute specifications

How do I create a link that opens a new window?

You can also parameterize the function to make it versatile, functional in more situations, therefore re-usable in scripts and webpages:

<script type="text/javascript">
var windowObjectReference = null; // global variable
function openRequestedPopup(url, windowName) {
  if(windowObjectReference == null || windowObjectReference.closed) {
    windowObjectReference = window.open(url, windowName, "popup");
  } else {
    windowObjectReference.focus();
  };
}
</script>
(...)
<p><a
 href="http://www.spreadfirefox.com/"
 target="PromoteFirefoxWindow"
 onclick="openRequestedPopup(this.href, this.target); return false;"
 title="This link will create a new window or will re-use an already opened one"
>Promote Firefox adoption</a></p>

You can also make such function able to open only 1 secondary window and to reuse such single secondary window for other links in this manner:

<script type="text/javascript">
var windowObjectReference = null; // global variable
var PreviousUrl; /* global variable that will store the
                    url currently in the secondary window */
function openRequestedSinglePopup(url) {
  if(windowObjectReference == null || windowObjectReference.closed) {
    windowObjectReference = window.open(url, "SingleSecondaryWindowName",
         "popup");
  } else if(PreviousUrl != url) {
    windowObjectReference = window.open(url, "SingleSecondaryWindowName",
      "popup");
    /* if the resource to load is different,
       then we load it in the already opened secondary window and then
       we bring such window back on top/in front of its parent window. */
    windowObjectReference.focus();
  } else {
    windowObjectReference.focus();
  };
  PreviousUrl = url;
  /* explanation: we store the current url in order to compare url
     in the event of another call of this function. */
}
</script>
(...)
<p><a
 href="http://www.spreadfirefox.com/"
 target="SingleSecondaryWindowName"
 onclick="openRequestedSinglePopup(this.href); return false;"
 title="This link will create a new window or will re-use an already opened one"
>Promote Firefox adoption</a></p>
<p><a
 href="https://www.mozilla.org/support/firefox/faq"
 target="SingleSecondaryWindowName"
 onclick="openRequestedSinglePopup(this.href); return false;"
 title="This link will create a new window or will re-use an already opened one"
>Firefox FAQ</a></p>

How can I prevent the confirmation message asking the user whether they want to close the window?

You cannot. New windows not opened by JavaScript cannot as a rule be closed by JavaScript. The JavaScript Console in Mozilla-based browsers will report the warning message: "Scripts may not close windows that were not opened by script." Otherwise the history of URLs visited during the browser session would be lost.

More on the window.close() method.

How can I bring back the window if it is minimized or behind another window?

First check for the existence of the window object reference of such window and if it exists and if it has not been closed, then use the focus() method. There is no other reliable way. You can examine an example explaining how to use the focus() method.

How do I force a maximized window?

You cannot. All browser manufacturers try to make the opening of new secondary windows noticed by users and noticeable by users to avoid confusion, to avoid disorienting users.

How do I turn off window resizability or remove toolbars?

You cannot force this. Users with Mozilla-based browsers have absolute control over window functionalities like resizability, scrollability and toolbars presence via user preferences in about:config. Since your users are the ones who are supposed to use such windows (and not you, being the web author), the best is to avoid interfering with their habits and preferences. We recommend to always set the resizability and scrollbars presence (if needed) to yes to insure accessibility to content and usability of windows. This is in the best interests of both the web author and the users.

How do I resize a window to fit its content?

You cannot reliably because the users can prevent the window from being resized by setting dom.disable_window_move_resize to true in about:config or by editing accordingly their user.js file.

In general, users usually disable moving and resizing of existing windows because allowing authors' scripts to do so has been abused overwhelmingly in the past and the rare scripts that do not abuse such feature are often wrong, inaccurate when resizing the window. 99% of all those scripts disable window resizability and disable scrollbars when in fact they should enable both of these features to allow a cautious and sane fallback mechanism if their calculations are wrong.

The window method sizeToContent() can also be disabled. Moving and resizing a window remotely on the user's screen via script will very often annoy the users, will disorient the user, and will be wrong at best. The web author expects to have full control of (and can decide about) every position and size aspects of the users' browser window ... which is not true.

How do I know whether a window I opened is still open?

You can test for the existence of the window object reference which is the returned value in case of success of the window.open() call and then verify that windowObjectReference.closed return value is false.

How can I tell when my window was blocked by a popup blocker?

With the built-in popup blockers, you have to check the return value of window.open(): it will be null if the window wasn't allowed to open. However, for most other popup blockers, there is no reliable way.

What is the JavaScript relationship between the main window and the secondary window?

The window.open() method gives a main window a reference to a secondary window; the opener property gives a secondary window a reference to its main window.

I cannot access the properties of the new secondary window. I always get an error in the JavaScript console saying "Error: uncaught exception: Permission denied to get property <property_name or method_name>. Why is that?

It is because of the cross-domain script security restriction (also referred as the "Same Origin Policy"). A script loaded in a window (or frame) from a distinct origin (domain name) cannot get nor set properties of another window (or frame) or the properties of any of its HTML objects coming from another distinct origin (domain name). Therefore, before executing a script targeting a secondary window, the browser in the main window will verify that the secondary window has the same domain name.

More reading on the cross-domain script security restriction: http://www.mozilla.org/projects/secu...me-origin.html

Generally speaking, it is preferable to avoid resorting to window.open() for several reasons:

• Most modern desktop browsers offer tab-browsing, and tab-capable browser users overall prefer opening new tabs than opening new windows in a majority of webpage situations.
• Most modern browsers offers a popup-blocking feature.
• Users can be using browser-built-in feature or extensions include opening a link in a new window or not, in the same window, in a new tab or not, in "background" or not. Coding carelessly to open new windows can no longer be assured of success, cannot succeed by force and, if it does, it will annoy a majority of users.
• New windows can have menubar missing, scrollbars missing, status bar missing, window resizability disabled, etc.; new tabs cannot be missing those functionalities or toolbars (or at least, the toolbars that are present by default). Therefore, tab-browsing is preferred by a lot of users because the normal user-interface of the browser window they prefer is kept intact, remains stable.
• Opening new windows, even with reduced features, uses considerably a lot of the user's system resources (cpu, RAM) and involves considerably a lot of coding in the source code (security management, memory management, various code branchings sometimes quite complex, window frame/chrome/toolbars building, window positioning and sizing, etc.). Opening new tabs is less demanding on the user's system resources (and faster to achieve) than opening new windows.

If you want to offer to open a link in a new window, then follow tested and recommendable usability and accessibility guidelines:

Never use this form of code for links: <a href="javascript:window.open(...)" ...>

"javascript:" links break accessibility and usability of webpages in every browser.

• "javascript:" pseudo-links become dysfunctional when JavaScript support is disabled or inexistent. Several corporations allow their employees to surf on the web but under strict security policies: no JavaScript enabled, no Java, no ActiveX, no Flash. For various reasons (security, public access, text browsers, etc..), about 5% to 10% of users on the web surf with JavaScript disabled.
• "javascript:" links will interfere with advanced features in tab-capable browsers: eg. middle-click on links, Ctrl+click on links, tab-browsing features in extensions, etc.
• "javascript:" links will interfere with the process of indexing webpages by search engines.
• "javascript:" links interfere with assistive technologies (e.g. voice browsers) and several web-aware applications (e.g. PDAs and mobile browsers).
• "javascript:" links also interfere with "mouse gestures" features implemented in browsers.
• Protocol scheme "javascript:" will be reported as an error by link validators and link checkers.

Further reading:

• Top Ten Web-Design Mistakes of 2002, 6. JavaScript in Links, Jakob Nielsen, December 2002
• Links & JavaScript Living Together in Harmony, Jeff Howden, February 2002
• comp.lang.javascript newsgroup discussion FAQ on "javascript:" links

Never use <a href="#" onclick="window.open(...);">

Such pseudo-link also breaks accessibility of links. Always use a real URL for the href attribute value so that if JavasScript support is disabled or inexistent or if the user agent does not support opening of secondary window (like MS-Web TV, text browsers, etc), then such user agents will still be able to load the referenced resource according to its default mode of opening/handling a referenced resource. This form of code also interferes with advanced features in tab-capable browsers: eg. middle-click on links, Ctrl+click on links, Ctrl+Enter on links, "mouse gestures" features.

Always identify links that will create (or will re-use) a new, secondary window

Identify links that will open new windows in a way that helps navigation for users by coding the title attribute of the link, by adding an icon at the end of the link or by coding the cursor accordingly.

The purpose is to warn users in advance of context changes to minimize confusion on the user's part: changing the current window or popping up new windows can be very disorienting to users (Back toolbar button is disabled).

"Users often don't notice that a new window has opened, especially if they are using a small monitor where the windows are maximized to fill up the screen. So a user who tries to return to the origin will be confused by a grayed out Back button." quote from The Top Ten New Mistakes of Web Design: 2. Opening New Browser Windows, Jakob Nielsen, May 1999

When extreme changes in context are explicitly identified before they occur, then the users can determine if they wish to proceed or so they can be prepared for the change: not only they will not be confused or feel disoriented, but more experienced users can better decide how to open such links (in a new window or not, in the same window, in a new tab or not, in "background" or not).

References

• "If your link spawns a new window, or causes another windows to 'pop up' on your display, or move the focus of the system to a new FRAME or Window, then the nice thing to do is to tell the user that something like that will happen." World Wide Web Consortium Accessibility Initiative regarding popups
• "Use link titles to provide users with a preview of where each link will take them, before they have clicked on it." Ten Good Deeds in Web Design, Jakob Nielsen, October 1999
• Using Link Titles to Help Users Predict Where They Are Going, Jakob Nielsen, January 1998

Always use the target attribute

If JavaScript support is disabled or non-existent, then the user agent will create a secondary window accordingly or will render the referenced resource according to its handling of the target attribute: e.g. some user agents that cannot create new windows, like MS Web TV, will fetch the referenced resource and append it at the end of the current document. The goal and the idea is to try to provide - not impose - to the user a way to open the referenced resource, a mode of opening the link. Your code should not interfere with the features of the browser at the disposal of the user and your code should not interfere with the final decision resting with the user.

Do not use target="_blank"

Always provide a meaningful name to your target attribute and try to reuse such target attribute in your page so that a click on another link may load the referenced resource in an already created and rendered window (therefore speeding up the process for the user) and therefore justifying the reason (and user system resources, time spent) for creating a secondary window in the first place. Using a single target attribute value and reusing it in links is much more user resources friendly as it only creates one single secondary window, which is recycled. On the other hand, using "_blank" as the target attribute value will create several new and unnamed windows on the user's desktop that cannot be recycled, reused. In any case, if your code is well done, it should not interfere with the user's final choice but rather merely offer them more choices, more ways to open links and more power to the tool they are using (a browser).

Opener window, parent window, main window, first window

Terms often used to describe or to identify the same window. It is the window from which a new window will be created. It is the window on which the user clicked a link that leads to the creation of another, new window.

Sub-window, child window, secondary window, second window

Terms often used to describe or to identify the same window. It is the new window that was created.

Unrequested popup windows

Script-initiated windows opening automatically without the user's consent.

Most modern browsers (listed below) don't allow web content to control the visibility of UI parts separately.

• Firefox 76 or newer
• Google Chrome
• Safari
• Chromium Edge

UI-related items of windowFeatures are used as a condition to whether opening a popup or a new tab, or a new window, and UI parts visibility of each of them is fixed.

The condition is described in detail in the "To check if a popup window is requested" section in the spec.

When content overflows window viewport dimensions, then scrollbar(s) (or some scrolling mechanism) are necessary to ensure that content can be accessed by users. Content can overflow window dimensions for several reasons that are outside the control of web authors:

• user resizes the window
• user increases the text size of fonts via View/Text Zoom (%) menuitem in Mozilla or View/Text Size/Increase or Decrease in Firefox
• user sets a minimum font size for pages that is bigger than the font-size the web author requested. People over 40 years old or with particular viewing habit or reading preference often set a minimal font size in Mozilla-based browsers.
• web author is not aware of default margin (and/or border and/or padding) values applying to root element or body node in various browsers and various browser versions
• user uses an user stylesheet (userContent.css in Mozilla-based browsers) for his viewing habits that increases document box dimensions (margin, padding, default font size)
• user can customize individually the size (height or width) of most toolbars via operating system settings. E.g. window resizing borders, height of browser titlebar, menubar, scrollbars, font size are entirely customizable by the user in Windows XP operating system. These toolbars dimensions can also be set via browser themes and skins or by operating system themes
• web author is unaware that the user default browser window has custom toolbar(s) for specific purpose(s); e.g.: prefs bar, web developer bar, accessibility toolbar, popup blocking and search toolbar, multi-feature toolbar, etc.
• user uses assistive technologies or add-on features that modify the operating system's work area for applications: e.g. MS-Magnifier
• user repositions and/or resizes directly or indirectly the operating system's work area for applications: e.g. user resizes the Windows taskbar, user positions the Windows taskbar on the left side (arabic language based) or right side (Hebrew language), user has a permanent MS-Office quick launch toolbar, etc.
• some operating system (macOS) forces presence of toolbars that can then fool the web author's anticipations, calculations of the effective dimensions of the browser window

Requested position and requested dimension values in the features list will not be honored and will be corrected if any of such requested value does not allow the entire browser window to be rendered within the work area for applications of the user's operating system. No part of the new window can be initially positioned offscreen. This is by default in all Mozilla-based browser releases.

MSIE 6 SP2 has a similar error correction mechanism but it is not activated by default in all security levels: a security setting can disable such error correction mechanism.