By Opera Software

From Opera 15 onward, Opera 11 & 12’s extension format is no longer supported, and instead, we’ve switched to Chromium’s extension model. Check out our new documentation for developing extensions for Opera 15 and higher and start building your own extensions.


The readonly id attribute a unique identifier for this browser tab. The value is a string of characters determined by the implementation and is unique for each browsing session.


readonly DOMString id


The following example creates a button on the browser toolbar. When the button is clicked, the ID of the currently selected tab is displayed in the button's badge.

// The background process (e.g. index.html)

// Specify the properties of the button before creating it.
var UIItemProperties = {
  disabled: false,
  title: "Example extension",
  icon: "images/icon_18.png",
  badge: {
    backgroundColor: '#cc0000',
    color: '#ffffff'

// Create the button and add it to the toolbar.
var button = opera.contexts.toolbar.createItem( UIItemProperties );

button.addEventListener('click', handleClick, false);

function handleClick() {
  // Get the currently selected tab
  var thisTab = opera.extension.tabs.getSelected();

  // Display the tab's ID in the button's badge
  button.badge.textContent =;

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