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To share an image made with an HTML canvas on iOS, export the canvas as a Blob, wrap it in a File, check that the browser can share that file, and call navigator.share() from a button tap. Keep a download or save option available: file sharing is not supported in every browser context, and a user can cancel the share sheet.
1. Export the canvas as a shareable image file
The Web Share API accepts a File for file sharing. Use canvas.toBlob() to encode the canvas, then create a File with a filename and MIME type that match the encoded image.
function canvasToFile(canvas) {
return new Promise((resolve, reject) => {
canvas.toBlob((blob) => {
if (!blob) {
reject(new Error("Canvas image export failed"));
return;
}
const type = blob.type || "image/png";
const extension = type === "image/jpeg" ? "jpg" : "png";
resolve(new File([blob], `canvas-image.${extension}`, { type }));
}, "image/png");
});
}This example requests PNG output. If you change the requested format, make sure the filename extension and the Blob’s MIME type describe the actual encoded file.
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Check both API presence and file support. navigator.share being available does not establish that the browser can share a particular file. navigator.canShare() is the capability check; pass it an object containing the files property, as documented by MDN.
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function canShareFile(file) {
return typeof navigator.share === "function" &&
typeof navigator.canShare === "function" &&
navigator.canShare({ files: [file] });
}A false result means the page should offer another way to retrieve the image instead of opening the share flow.
3. Call the share API from the user’s tap
Web Share requires a secure context and transient user activation. In practice, invoke navigator.share() directly in the Share button’s click handler; waiting for slow work before calling it can lose the required activation. WebKit’s explanation of user activation describes the direct-interaction requirement at The User Activation API.
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If creating the file takes time, prepare it after the canvas is finalized and store it in application state. Then the tap handler can share the already-prepared file:
let readyFile = null;
// Call after the canvas content is finalized.
canvasToFile(canvas)
.then((file) => { readyFile = file; })
.catch((error) => { console.error(error); });
shareButton.addEventListener("click", async () => {
if (!readyFile || !canShareFile(readyFile)) {
showSaveOption();
return;
}
try {
await navigator.share({ files: [readyFile] });
} catch (error) {
if (error.name === "AbortError") {
// The user canceled, or no share target was available.
return;
}
showSaveOption();
}
});The Web Share API invokes the platform’s native sharing mechanism; the user chooses a destination, and opening the share sheet does not prove the image was delivered. See MDN’s Navigator.share() reference for supported data and documented promise outcomes.
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4. Keep a save or download fallback
Offer a separate way to save the generated image if file sharing is unavailable or fails. A simple download link can use the same File:
function downloadFile(file) {
const url = URL.createObjectURL(file);
const link = document.createElement("a");
link.href = url;
link.download = file.name;
link.click();
URL.revokeObjectURL(url);
}Present the fallback when the capability check fails or a non-cancellation error occurs. Treat cancellation as an ordinary user choice rather than a delivery failure; MDN documents AbortError for a canceled share or when no target is available.
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5. Check page context and diagnose failures
- Secure context: Web Share is restricted to secure contexts. Test the deployed page in the browser context your users will use.
- Permissions Policy: The
web-sharedirective can block access. Its default allowlist isself; an embedded page may need explicit delegation from its parent. A policy block can result inNotAllowedError. See MDN’s web-share Permissions-Policy reference. - User activation: Make the call in response to the tap, not after an unrelated delay or lengthy asynchronous operation.
- File capability: Test the actual File with
navigator.canShare({ files: [file] }); API presence alone is not enough. - Outcome handling: Do not tell users the image was sent just because the native sheet appeared. The selected target controls what happens next.
What to expect from iOS browsers and share targets
WebKit announced navigator.share() for Safari 12.1 as a way to invoke the operating system’s native sharing dialog (Safari 12.1 feature announcement). That historical support announcement does not guarantee identical file-sharing behavior across every current iOS browser shell, embedded view, image type, or destination app.
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Older WebKit issue reports describe two specific edge cases: a Safari 15/iOS 15 report filed in April 2022 concerned a share promise that did not resolve after choosing Save Image (WebKit report); a 2023 report described image-plus-text sharing in which the text was ignored (WebKit report). These reports establish that such behavior was reported in older implementations, not whether either issue persists in current iOS releases. Test the iOS versions and destination apps you intend to support, especially when sharing a file together with text or a URL.
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