How to set a Blob as the " src " of an iframe

In web development, sometimes we need to display dynamically generated content, such as PDF files or images created on the client side, directly within an iframe. When the content is binary data, we can handle it using a Blob object, then convert this Blob object into a URL and assign it to the src attribute of the iframe.

Steps:

1. Create a Blob object: First, create a Blob object. Blob objects can be constructed in various ways, such as from ArrayBuffer or byte arrays.

   javascript
   const blob = new Blob(['Hello, world!'], { type: 'text/plain' });

2. Create a Blob URL: Use the URL.createObjectURL() method to convert the Blob object into a URL that can be accessed. This method generates a unique URL pointing to the Blob object in memory.

   javascript
   const blobUrl = URL.createObjectURL(blob);

3. Set the iframe's src: Assign the generated URL to the src attribute of the iframe.

   html
   <iframe src="" id="myiframe"></iframe>
   <script>
       document.getElementById('myiframe').src = blobUrl;
   </script>

Security Considerations:

• When using Blob URLs, since the URL points to local resources on the client side, it is generally considered safe, but you must ensure the Blob content is trusted to prevent XSS attacks.

Releasing the Blob URL: When no longer needed, use URL.revokeObjectURL() to release the URL so the browser can reclaim associated resources.

javascript
URL.revokeObjectURL(blobUrl);

Usage Scenario Example:

Suppose we need to generate an image on the client side and display it within an iframe.

javascript
const canvas = document.createElement('canvas');
const ctx = canvas.getContext('2d');

// Draw a simple red rectangle
ctx.fillStyle = 'red';
ctx.fillRect(10, 10, 50, 50);

// Convert the Canvas to a Blob
canvas.toBlob(function(blob) {
    const url = URL.createObjectURL(blob);
    document.getElementById('myiframe').src = url;

    // Release the URL when appropriate
    // URL.revokeObjectURL(url);
}, 'image/png');

In the above code, we create a canvas, draw a shape, convert it to a Blob, and finally display it within the iframe. This approach is suitable for dynamically generated content, such as client-side image processing or PDF generation.