Hoe to Pass an Event to an iframe from the parent window using Javascript?

In JavaScript, passing events from the parent window to an embedded iframe requires specific steps and security measures to ensure proper code execution and data security. The following is a systematic approach to achieve this functionality:

Step One: Ensure Same-Origin Policy

First, ensure that both the parent window and the iframe comply with the same-origin policy (i.e., the protocol, domain, and port are identical). If they are not same-origin, the browser's security policy will block cross-origin communication unless techniques such as postMessage are employed.

Step Two: Use postMessage Method

postMessage is a method introduced in HTML5 that enables secure communication between windows from different origins. It can send messages to another window regardless of whether the window shares the same origin. To send data or notification events from the parent window to the iframe, use the following code:

javascript
// In parent window
var iframe = document.getElementById('myIframe');
var message = "Hello from parent!";  // Message to send
iframe.contentWindow.postMessage(message, 'http://example.com');

Step Three: Receive Messages in Iframe

In the iframe, set up an event listener to receive and process messages from the parent window:

javascript
// In iframe
window.addEventListener('message', function(event) {
    if (event.origin !== "http://example.com") {
        // If origin does not match, ignore the message
        return;
    }

    console.log('Message received in iframe: ', event.data);
    // Process the message based on event.data
});

Example

Assume we have a parent page containing an embedded iframe from the same origin, and we need to notify the iframe when a user clicks a button on the parent page:

Parent Page HTML:

html
<button id="notifyButton">Notify Iframe</button>
<iframe id="myIframe" src="http://example.com/iframe.html"></iframe>

Parent Page JavaScript:

javascript
document.getElementById('notifyButton').addEventListener('click', function() {
    var iframe = document.getElementById('myIframe');
    iframe.contentWindow.postMessage("User clicked button", "http://example.com");
});

Iframe Page JavaScript:

javascript
window.addEventListener('message', function(event) {
    if (event.origin === "http://example.com") {
        alert("Received notification: " + event.data);
    }
});

Through this example, when a user clicks the button, the iframe receives a notification displayed as an alert. This is an effective way to securely pass data and notify events between different frames.