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 1Edge Full support 12Firefox Full support 1
Full support 1
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 Full support 4Opera Full support ≤12.1Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support ≤12.1Safari iOS Full support 1Samsung Internet Android Full support 1.0


Full support  
Full support
See implementation notes.
See implementation notes.