by In the realm of web development, iframes have long been an essential tool for integrating content from one website into another. Whether it’s by embedding a video, displaying a map, or showcasing an external application, iframes provide a convenient way to load content from another website within a page.
However, there’s always room for improvement. In this blog post, we will explore the challenges posed by predefined fixed-height iframes with scroll bars and how we can enhance the user experience by making the iframe height dynamic based on its content, enabling seamless integration without visible indications of external sourcing.
The Problem:
During our work on a project that heavily utilized iframes we encountered an issue that hindered the seamless integration of external content. We observed that, the presence of fixed heights and scroll bars within the iframes created a barrier to achieving cohesive integration.
To solve this issue, we aimed to create an illusion where the content within the iframe appeared as if it were an inherent part of our website without any visible indication that it originated from a different source. To achieve this, we needed to eliminate the scroll bar and dynamically adjust the iframe’s height based on its content, ensuring a cohesive and uninterrupted user experience.
The First Solution: Security Hurdles:
The first approach that came to our minds was to access the document within the iframe, retrieve its height, and subsequently update the iframe’s height accordingly. However, we soon discovered that accessing the document of an iframe directly from the parent page is not possible due to security restrictions.
These security restrictions exist to protect users from potential security vulnerabilities. They prevent cross-origin manipulation, meaning that code from one domain cannot access or modify the content of an iframe originated from a different domain. This safeguard is crucial in preventing malicious actors from tampering with sensitive information or executing harmful actions within iframes.
Cross-origin security restrictions are enforced by web browsers through a mechanism called the Same-Origin Policy (SOP). The SOP ensures that web pages from different origins (domains, protocols, and ports) are isolated from each other for security reasons. By enforcing the SOP, browsers restrict direct access to the document and content of iframes that originate from a different domain.
While it is possible to overcome the SOP by allowing specific domains through CORS (Cross-Origin Resource Sharing) headers, we deliberately chose not to pursue this route. We wanted to find a solution that was agnostic to the parent using the iframe. This decision was driven by our desire for a more flexible and scalable approach, without the need to add a new domain to the list every time we needed to use the iframe on a new project or website.
We aimed to create a solution that could seamlessly integrate the iframe’s content into various projects without the hassle of configuring domain-specific settings. By taking this approach, we could ensure that our solution was not dependent on specific domain configurations, making it easier to implement and maintain in the long run.
Creating Communication Channels:
Intending to find an alternative solution that would overcome the security hurdles imposed by the SOP, we explored other methods and APIs. This led us to the discovery of the window.parent object, which provides a secure means to establish communication between the iframe and the parent page, regardless of the specific domain configurations.
The window.parent object refers to the parent window or the window that contains the iframe. It provides a mean for communication and interaction between the iframe and the parent page. By accessing the window.parent object from within the iframe, we can invoke methods and access properties of the parent window.
One such method that becomes crucial in this context is the postMessage method. The postMessage method allows for secure cross-origin communication between windows or frames. It enables the exchange of data and messages between the iframe and the parent page.
window.parent.postMessage(event, targetOrigin);The postMessage function requires a minimum of two parameters. The first parameter is the message to be sent, and the second parameter is the targetOrigin. The targetOrigin specifies the expected origin of the receiving window or target window. It can be set as a string literal "*" or as a URI. When set as "*", it indicates that there is no specific preference for the origin, allowing the message to be dispatched to any window that is listening for messages.
When the postMessage method is called from within the iframe, it sends a message to the parent page. The message can then be captured by the parent page through an event listener that is set up to listen for messages. This event listener can be attached to the window object of the parent page.
On the parent page, we implemented a message listener that captures the messages sent from the iframe using the postMessage method. Within this message listener, we can extract the necessary information from the message, such as the scrollHeight of the iframe’s content, and then update the iframe’s height accordingly.
window.addEventListener('message', handleReceiveMessage);By utilizing the window.parent.postMessage method, we were able to establish a secure communication channel between the iframe and the parent page. This allowed us to exchange data and instructions, enabling the dynamic adjustment of the iframe’s height based on its content.
Addressing Content Changes with MutationObserver:
While sending a single message resolved the initial problem, we realized that it wasn’t sufficient to handle scenarios where the content inside the iframe might change dynamically. We needed a way to detect and respond to these changes automatically. This is where the MutationObserver comes into play.
The MutationObserver is a powerful JavaScript API that allows us to observe and respond to changes in the DOM (Document Object Model). It provides a mechanism for tracking modifications to the structure and content of an HTML document, including additions, removals, and modifications of nodes.
By using the MutationObserver, we can actively monitor the content within the iframe and trigger actions whenever changes occur. This is especially useful when the content inside the iframe is dynamic and can be altered by user interactions, external events, or even asynchronous updates.
To use the MutationObserver, we first instantiate a new instance of it by passing a callback function as the argument. This callback function is executed whenever a change is detected. Within the callback function, we can define the actions we want to take in response to the observed changes.
const observer = new MutationObserver(handleDocumentMutation);Next, we specify the target node that we want to observe. In our case, the target node is the content document within the iframe. By targeting the content document, we can track any modifications made to the HTML elements, text nodes, or attributes within the iframe.
const observer = new MutationObserver(handleDocumentMutation);
observer.observe(document.body, options);By passing the options object we can also define the specific types of mutations we are interested in observing. This allows us to narrow down the scope and only react to relevant changes. For example, we might choose to observe mutations related to the addition or removal of child nodes, attribute modifications, or even changes to the content of specific elements. Here you can read more about the options that can be passed. In our case we are using the following options:
const observer = new MutationObserver(handleDocumentMutation);
observer.observe(document.body, {
subtree: true,
attributes: true,
childList: true,
characterData: true
});When a mutation occurs that matches our defined criteria, the callback function is triggered. Within the callback function, we can perform actions such as extracting the updated scrollHeight of the iframe’s content and sending a message to the parent page using the postMessage method, similar to what we discussed earlier.
By combining the power of the MutationObserver with the postMessage method, we can ensure that the parent page stays in sync with the dynamically changing content inside the iframe. This allows us to continuously update the iframe’s height to provide a seamless user experience, even when the content within the iframe undergoes modifications.
The Final code:
Inside the page that is going to be used as an iframe we start by initializing a currentDocumentHeight variable to keep track of the current height of the document within the iframe. Then we define a sendMessageUpdatingHeight function, which takes a height parameter and sends a message to the parent page using the postMessage method. The message contains an event name "SET_HEIGHT" and a payload object containing the updated height.
After that the handleDocumentMutation is created for monitoring changes in the document. It retrieves the current height of the document using document.body.scrollHeight and compares it with the currentDocumentHeight. If the document height has changed, the currentDocumentHeight is updated, and the sendMessageUpdatingHeight function is called.
Then we create a new MutationObserver and pass the handleDocumentMutation function as the callback. It observes mutations in the document, so any changes that affect the height of the document will trigger the handleDocumentMutation function and update the iframe’s height through the sendMessageUpdatingHeight function.
let currentDocumentHeight = 0;
const sendMessageUpdatingHeight = (height) => {
window.parent.postMessage({ eventName: 'SET_HEIGHT', payload: { height } }, '*');
};
const handleDocumentMutation = () => {
const documentHeight = document.body.scrollHeight;
if (documentHeight && documentHeight !== currentDocumentHeight) {
currentDocumentHeight = documentHeight;
sendMessageUpdatingHeight(documentHeight);
}
};
const observer = new MutationObserver(handleDocumentMutation);
observer.observe(document.body, {
subtree: true,
attributes: true,
childList: true,
characterData: true
});In the parent page we start by initializing a currentIFrameHeight variable to keep track of the current height of the iframe. Then we define a handleReceiveMessage function as the event handler for the message event. It takes an event parameter, which represents the message sent by the iframe page. The handleReceiveMessage function extracts the eventName and payload properties from the event.data object. The eventName represents the type of message received, and the payload contains additional data associated with the message.
Then we need to check if the event captured is the one we are expecting, we do that by checking if the eventName is equal to "SET_HEIGHT". We also need to make sure that the payload includes a valid height property. Only then the currentIFrameHeight variable is updated with the new height value. Lastly, the window.addEventListener method is used to attach the handleReceiveMessage function to the message event of the window object, enabling the page to listen for incoming messages from the iframe.
let currentIFrameHeight = 0;
const handleReceiveMessage = (event) => {
const eventName = event?.data?.eventName;
const payload = event?.data?.payload;
if (eventName === 'SET_HEIGHT' && payload?.height) {
currentIFrameHeight = payload.height;
}
};
window.addEventListener('message', handleReceiveMessage);Conclusion:
Enhancing the user experience with dynamic iframe height provides a solution to the challenges posed by fixed-height iframes with scroll bars. By eliminating scroll bars and seamlessly integrating content, a more cohesive user experience is achieved.
After exploring the use of the window.parent object and the postMessage method we were able to establish a secure communication channel between the iframe and the parent page. This allows for the dynamic adjustment of the iframe’s height based on its content, providing a seamless integration without visible indications of external sourcing.
Additionally, the MutationObserver API is utilized to detect and respond to changes in the iframe’s content, ensuring that the parent page stays in sync with dynamic updates. By combining these techniques, web developers can create a more immersive and uninterrupted browsing experience for users.
In conclusion, the implementation of dynamic iframe height enhances the user experience by eliminating scroll bars and seamlessly integrating content. By leveraging the window.parent object, the postMessage method, and the MutationObserver API, developers can achieve a cohesive and immersive user experience. These techniques provide flexibility and scalability, as they do not rely on domain-specific configurations, making them easily implementable and maintainable across various projects and websites. With dynamic iframe height, users can enjoy a seamless integration of external content, creating a more engaging and cohesive browsing experience.
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