The Window.resizeBy() method resizes the current window by a specified amount.


window.resizeBy(xDelta, yDelta) 


  • xDelta is the number of pixels to grow the window horizontally.
  • yDelta is the number of pixels to grow the window vertically.


// Shrink the window 
window.resizeBy(-200, -200);


This method resizes the window relative to its current size. To resize the window in absolute terms, use window.resizeTo().

Creating and resizing an external window


For security reasons, it's no longer possible in Firefox for a website to change the default size of a window in a browser if the window wasn’t created by, or contains more than one tab. See the compatability table for details on the change.

Even if you create window by it is not resizable by default. To make the window resizable, you must open it with the "resizable" feature.


// Create resizable window
myExternalWindow ="http://myurl.domain", "myWindowName", "resizable");

// Resize window to 500x500
myExternalWindow.resizeTo(500, 500);

// Make window relatively smaller to 400x400
myExternalWindow.resizeBy(-100, -100);

The window you create must respect the Same Origin Policy. If the window you open is not in the same orgin as the current window, you will not be able to resize, or access any information on, that window/tab.


Specification Status Comment
CSS Object Model (CSSOM) View Module
The definition of 'window.resizeBy()' in that specification.
Working Draft  

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
resizeByChrome Full support YesEdge Full support 12Firefox Full support Yes
Full support Yes
Notes Since Firefox 7, it's no longer possible for a web site to change the default size of a window in a browser if the window wasn't created by or contains more than one tab. See here for more details.
IE ? Opera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesFirefox Android Full support YesOpera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yes


Full support  
Full support
Compatibility unknown  
Compatibility unknown
See implementation notes.
See implementation notes.