Progressive image decoding can help a browser present surrounding content without waiting for an image to be decoded, but it does not make the image download faster. Use decoding="async" selectively when other content should paint first; use JavaScript’s HTMLImageElement.decode() when a script needs to wait for a particular image before showing it. For many static images, leaving the browser’s default auto choice alone is reasonable.
What progressive image decoding changes
The HTML decoding attribute is a browser scheduling hint. It influences how image decoding is coordinated with presentation; it does not speed up the network request, compress an image, or guarantee a faster page.
With decoding="async", the browser is permitted to paint other content before the image has been decoded and presented. That can avoid making surrounding content wait on image decoding. MDN summarizes the behavior as: “In practice, async means that the next paint does not wait for the image to decode.” The observable effect can be subtle with ordinary static markup and more relevant when JavaScript inserts or swaps images.
Choose between async, sync, auto, and decode()
| Option | What it asks or enables | When it fits |
|---|---|---|
decoding="async" |
Allows the browser to present other content before decoding and presenting the image. | Use selectively when surrounding content should not be held up by that image. |
decoding="sync" |
Asks the browser to coordinate image decoding with rendering of related content. | Consider only when coordinated presentation is important; measure the result in the target browsers. |
decoding="auto" |
Leaves the choice to the browser. This is the default choice. | Keep it when you have no specific reason to direct scheduling. |
HTMLImageElement.decode() |
Returns a promise that resolves when that image has decoded. | Use in JavaScript when an image should not be inserted or revealed until it is ready. |
None is universally fastest. The useful choice depends on whether the image is static or dynamically changed, whether surrounding content or coordinated presentation matters more, and what happens in the browsers and workload you actually support. No universal numeric improvement from async is established.
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
Use async selectively in static HTML
For an image where other content should be allowed to paint first, add the hint directly to the image:
<img src="/images/article-chart.webp" alt="Monthly results chart" width="1200" height="800" decoding="async">Do not add it everywhere just because the value says “async.” Leave the browser’s auto choice when there is no reason to change scheduling, and compare the actual rendering behavior before making a site-wide change.
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
Wait for a dynamically created image before showing it
When JavaScript swaps an image, showing the new element before it is ready can expose an empty or incomplete transition. Create the image, set its source, await decode(), and then replace the current content. Keep a fallback for a rejected promise, which can occur if loading or decoding fails.
async function revealImage(url, container) {
const img = new Image();
img.src = url;
try {
await img.decode();
container.replaceChildren(img);
} catch {
// Keep or show an existing fallback when loading or decoding fails.
}
}This coordinates the reveal of this image; it does not accelerate its request. In production, retain or display a meaningful fallback in the failure branch so the container does not become blank if the new image cannot be used.
Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
Do not confuse decoding with fetching or layout stability
Image performance has separate bottlenecks. Choose the control that addresses the one you have:
- Decoding:
decodinginfluences coordination between decoding and rendering. - Download timing:
loading="lazy"defers offscreen image fetching. Avoid applying it indiscriminately to an image likely to be needed in the initial viewport or to be the page’s Largest Contentful Paint image. - Request importance:
fetchpriorityadjusts an image request’s relative fetch priority; it is not a decoding setting. - Layout shifts: Provide
widthandheight, or otherwise reserve the intended space, particularly for lazy-loaded images. - Transfer cost: Use appropriately sized, compressed files and responsive source selection. A scheduling hint cannot compensate for unnecessarily large image bytes.
These approaches can be combined when each addresses a real need, but they solve different parts of the loading experience.
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
Measure before changing every image
Compare the current behavior with a targeted change on representative pages and browsers. Look at whether the image is static or dynamically swapped, whether nearby content paints sooner, whether the image presentation feels less coordinated, and whether layout stability or request timing changed. A value such as async is a hint rather than a guarantee, so do not infer a universal Core Web Vitals improvement from the attribute alone.
Or skip the browser setup
ScreenshotNeo is a website screenshot API and MCP server, not an image-decoding optimization. It can capture the rendered state of a page while you inspect how a page or image appears; it does not change the browser’s decoding schedule. Its clean-shot options accept consent banners and remove 60+ known consent platforms, newsletter popups, and chat widgets before capture, and each step can be turned off. Bot checks, blank pages, timeouts, failed loads, and cache hits are not billed; response headers identify the page verdict and billing status. An MCP server provides screenshot tools for AI agents. The free plan includes 1,000 screenshots a month with no card; paid plans start at $5 for 3,000. See the ScreenshotNeo API documentation.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpTry ScreenshotNeo if you need rendered page captures, and sign up for 1,000 free screenshots a month with no card.
Quick Recap
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
