Calling a parent window function from an iframe

javascript

cross-origin

event-listener

parent-child-communication

byAlex Kataev·Jan 31, 2025

To invoke a function in the parent window from an iframe use:

parent.functionName(); // Just like mom always said "clean your room", your parent window says "invoke your function."

Note:

Same-origin policy: Parent-child communication works only if the iframe and parent belong to the same origin.

Cross-origin: If they don't share the same origin, window.postMessage() is your friend:

// In the iframe:
parent.postMessage('secret message', 'https://parent-origin.com'); // Sending secret messages to the "parent"! 

// In the parent:
window.addEventListener('message', (event) => {
  if (event.origin === 'https://expected-iframe-origin.com') {
    // "I've been expecting you!" 
  }
});

Security Tip: Never forget to check the event.origin! Trust, but verify.

Facing errors and scope problems like a pro

Errors can turn up like uninvited party crashers. Here's how to show them the door:

Scope out the Console: That's where error messages like to party. "Uncaught TypeError" or "Access Denied" significantly implicate same-origin policy violations or syntax troubles.
Global Scope: Make sure your parent function is not a recluse and is freely accessible from the iframe.
Iframe Permissions: Sandbox attribute might limit your iframe's liberties. Ensure the permissions are set right.

Best practices for secure communication (don't be a wi-fi freeloader)

Remember these tips for secure communication:

Trust No One: Always verify the sender's origin especially in cross-origin scenarios. Don't expose sensitive functions to potentially shady sites.
Wildcards: They aren't so wild. In postMessage(), avoid '*' for targetOrigin and use the exact target origin.
Message Reception: Create a resilient event listener in the parent window to effectively handle various message types.
Scope Adjustment: Adjust document.domain if both the iframe and parent share the same second-level domain but be wary of security risks involved.

Smooth cross-domain conversations (and potential fallbacks)

Here's how to make your parent-iframe communication smoother than your internet connection:

Event Failure: Use window.parent.postMessage() when onclick events are blocked by content security policies.
Function Placement: Functions that the iframe needs should ideally be slotted in the parent's global scope.
Href Fallback: If onclick fails, roll back to invoking the JavaScript functions using the href attribute.

Compatibility: The key to domestic harmony

Just like maintaining a strong relationship, consistency is vital:

Same Doctype: Declare the same doctype in the parent and iframe documents to ensure the JavaScript execution context remains on the same page.
Subdomain Handshake: When embedding an iframe under a different subdomain, remember to consider cookie and local storage behaviors.

Tricky situations and how to avoid them

A fair share of problems may arise in the journey, but fret not! We've got you covered:

Event Listener Overflow: Don't forget to remove event listeners when no longer needed. Think of it as tidying up after a party.
Content Security Policies (CSP): CSP rules can often play spoilsport. Counter these restrictions by adjusting your CSP headers accordingly.
Iframe-sided love: When working with nested iframes, ensure messages are properly passed through each layer for a clear two-way communication.

explain-codes / Javascript / Calling a parent window function from an iframe

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