WebAssembly support for a web developer demo

Your demo works on your computer, but a visitor sees a blank panel, a loading spinner, or an error. If the demo uses WebAssembly, the browser must be able to load and run its module, but support is only one part of the check.

Use Browser Info to check the browser and its reported features. Then open the demo in that same browser and test the interaction it is meant to show. This helps separate a missing browser capability from a problem with the module, its download, or the demo itself.

Check WebAssembly support in the browser

1. Open Browser Info in the browser you plan to use for the demo. Check the browser version and engine, then look under supported features for WebAssembly or WASM, if it is listed.
2. Open the demo in a separate tab in the same browser. Wait for it to finish loading, then try the main action, such as starting the simulation or processing a sample.
3. Repeat the same action in another up-to-date browser if the demo fails. Use the same device, network, and demo URL so you can compare the browser behavior fairly.
4. Write down the browser name and version, what you clicked, and the exact error or point where loading stops. If you maintain the demo, check its browser console and network requests for the module's loading error.

Browser Info reports what the current browser exposes. It does not run your demo's WebAssembly module, verify that the module downloaded correctly, or measure how fast the demo will perform. The live demo is the practical compatibility check.

What the result means

WebAssembly is listed and the demo works

The browser reports the capability, and this demo's basic path works on this device. That is good evidence for this browser and version, but it is not proof that every feature or every visitor's device will work. Test the demo's important controls and any larger or more demanding sample before presenting it.

WebAssembly is listed, but the demo fails

The browser can support WebAssembly while the demo still has a separate problem. The module might not download, the response might have an incorrect content type, a cross-origin request might be blocked, or the demo may expect a browser API that is unavailable. Look at the browser console and network panel for a failed request or a specific error rather than treating the capability report as a complete diagnosis.

WebAssembly is not listed, or the feature report is unclear

A missing entry is not always proof that WebAssembly is disabled. Browser Info can only report features it checks and can identify in that browser. Update the browser, try the demo directly, and compare with another current browser. If only one browser fails, focus on its version, settings, extensions, or management policy.

The demo loads but feels slow

Support does not guarantee fast performance. A module can take time to download and initialize, and the work it performs may be too heavy for the device. The demo may also spend time moving data between WebAssembly and JavaScript, or updating the page. Try a smaller sample and compare on another device before concluding that the browser lacks support.

How to fix a demo that will not run

1. Update the browser. In Chrome or Edge, open the browser menu and go to its About page to check for updates. On Windows 11, also check Settings › Windows Update. On macOS, open System Settings › General › Software Update, which can also provide Safari updates.
2. Try a clean browser session. Open the demo in a private window or a new browser profile. If it works there, an extension, stored site data, or a changed browser setting may be interfering. Disable extensions one at a time to find the cause.
3. Check the module request. If you maintain the demo, inspect the network panel for a failed or blocked WebAssembly file. When using WebAssembly.instantiateStreaming(), the server should return the module with the application/wasm content type. A fallback loader may behave differently, so check the exact error before changing server settings.
4. Check cross-origin access. If the module is hosted on a different domain from the page, confirm that the server allows the browser's request. A blocked request can prevent a supported browser from ever receiving the module.
5. Check for a managed-browser restriction. On a work or school device, browser policies may limit features or block downloads. Ask the administrator whether the demo's site or module is restricted. Do not try to bypass a policy on a managed computer.
6. Offer a fallback for visitors. If some supported browsers or devices still cannot complete the demo, provide a simpler JavaScript path, a non-interactive preview, or clear instructions for a supported browser. Do not assume every visitor has the same browser, device, or network as the presenter.

What WebAssembly contributes to a demo

WebAssembly is a format that lets a browser run compiled code in a restricted environment. Developers often use it to bring existing code written in languages such as C, C++, or Rust to the web, or to handle demanding tasks like calculations, image processing, and simulations. JavaScript can still control the page and connect the module to browser features.

It is not a replacement for HTML, CSS, or JavaScript, and it does not automatically make every page faster. A simple interface may not benefit from it. For a live demo, the useful question is not just whether the browser supports WebAssembly, but whether the full experience loads, responds, and performs well on the devices your audience will use.

WebAssembly runs within the browser's security boundaries. The demo still needs browser APIs and user permissions for actions such as opening a file, recording audio, or using a camera.