Avoid using window.top

Category: Supportability, Upgrade readiness, Online migration

Impact potential: High


  • The following script error will be displayed to users or included in your error logs: Error: Blocked a frame with origin "https://<yourinstance>.dynamics.com" from accessing a cross-origin frame.

  • Customizations might not behave correctly in the context of Dynamics 365 App for Outlook, Dynamics 365 for phones and tablets, or an external application that hosts Microsoft Dataverse within an Iframe.


    There might be some scenarios where error handling masks the error and continues script processing, causing unexpected behavior.


Avoid using window.top in scripts running within the context of Dynamics 365 App for Outlook, Dynamics 365 for phones and tablets, or an external application that hosts Dataverse within an Iframe. Even if these scenarios don't currently apply to your organization, you should avoid using window.top or guard against this issue.


Usage of window.parent or variations of the parent hierarchy (for example,window.parent.parent) can cause the same symptoms.

The following are the recommended approaches:

  • Avoid usage of the window.top object altogether.

  • If using window.top is the only available option, first test to determine whether window.top is accessible by using the script below. If it's not available, provide alternate logic or a fallback user experience.


    Although we recommend that you avoid using window.top, this script is included for those edge cases where it might be the only option available.

    function isTopAccessible() {
        try {
                return true;
            catch (err) {
                return false;
    var canAccess = isTopAccessible();

Problematic patterns

Any usage of window.top should be avoided, if possible. The following are examples of commonly seen patterns.


These scenarios should be avoided.

// Getting or setting variables at the top level
var myValue = window.top.myGlobalVariable;

// Attempting to access the Xrm namespace at the top level
myValue = window.top.Xrm.Page.getAttribute("column1");

Additional information

In the scenarios mentioned, window.top refers to the window owned by an application context external to Dynamics 365. Due to the differing origins, the browser presents the user with a cross-origin security error.

See also

Apply business logic using client scripting in model-driven apps using JavaScript
Events in forms and grids in model-driven apps