devtools.panels.ElementsPanel.setExpression()

Evaluates an expression in the context of the inspected page, and displays the result in the extension sidebar pane.

The expression's execution context is the same as that for inspectedWindow.eval().

JSON objects and DOM nodes are displayed as an expandable tree, as in the JSON viewer in Firefox. You can optionally specify a rootTitle string: this will be displayed as the title of the tree's root.

This is an asynchronous function that returns a Promise.

Syntax

let evaluating = browser.devtools.panels.setExpression(
  expression,       // string
  rootTitle         // string
)

Parameters

expression: string. The expression to evaluate.
rootTitle Optional: string. The title of the root of the tree in which results are displayed.

Return value

A Promise that will be fulfilled with no arguments, once the expression has been evaluated.

Examples

This code creates a sidebar pane that displays the tagName of the currently selected element:

function onCreated(sidebarPane) {
  browser.devtools.panels.elements.onSelectionChanged.addListener(() => {
    const exp = "$0 && $0.tagName";
    const title = "Selected Element tagName";
    sidebarPane.setExpression(exp, title);
  });
}

browser.devtools.panels.elements.createSidebarPane("My pane").then(onCreated);

Browser compatibility

	desktop					mobile
	Chrome	Edge	Firefox	Opera	Safari	Firefox for Android	Safari on iOS
`setExpression`	Chrome – Full support Chrome 18 (Release date: 2012-03-28) footnote footnote The expression must evaluate to a JavaScript object or a DOM node, or nothing is shown in the sidebar.	Edge – Full support Edge 79 (Release date: 2020-01-15) footnote footnote The expression must evaluate to a JavaScript object or a DOM node, or nothing is shown in the sidebar.	Firefox – Full support Firefox 57 (Release date: 2017-11-14) footnote footnote Before Firefox 60, the expression must evaluate to an object that can be serialized to JSON, or nothing was shown in the sidebar. In particular, JavaScript cyclic objects and DOM nodes were not supported. See bug 1403130.	Opera – Full support Opera 15 (Release date: 2013-07-02) footnote footnote The expression must evaluate to a JavaScript object or a DOM node, or nothing is shown in the sidebar.	Safari – No support Safari footnote No support	Firefox for Android – No support Firefox for Android footnote No support	Safari on iOS – No support Safari on iOS footnote No support

Tip: you can click/tap on a cell for more information.

Full support: Full support
No support: No support
: See implementation notes.

Note: This API is based on Chromium's chrome.devtools.panels API.

This page was last modified on Jul 17, 2025 by MDN contributors.

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