Web Share API is a W3C browser interface that opens the device's native share sheet so a web page can pass a title, text, URL or files to an app the user picks. It adds navigator.share() and navigator.canShare(), and both exist only in secure contexts. The detail developers hit first is that share() must run inside a user gesture such as a click, or it rejects with NotAllowedError.
You call navigator.share(data) with a ShareData dictionary. Its members are title, text, url and files, and all are optional, though at least one must be present and valid. The method returns a promise. It resolves once the data has been handed to the chosen target or to the operating system, and it rejects if anything goes wrong or the user backs out.
The spec requires transient user activation and consumes it, so a second share() call needs a fresh click. The browser then shows its own picker, which acts as the security confirmation: a page cannot silently send data to a native app.
If url is present, the browser parses it against the page's base URL and shares the serialized result. An empty string therefore means the current page. The snippet below runs the same parsing rule with Node's URL class.
const page = "https://example.com/blog/post?id=7#top";
console.log(new URL("", page).href);
console.log(new URL("/blog/other", page).href);
console.log(new URL("https://example.com/a b", page).href);
try { new URL("http://", page); } catch (e) { console.log(e.name + ": " + e.message); }Output:
https://example.com/blog/post?id=7
https://example.com/blog/other
https://example.com/a%20b
TypeError: Invalid URLThe first line shows the fragment is dropped when the string is empty. A URL that cannot be parsed makes share() reject with a TypeError.
navigator.canShare(data) validates the same dictionary and returns a boolean. Unlike share(), it needs no user activation, so you can use it on page load to decide whether to show a Share button. Passing files is the main reason to call it, because file support varies by platform and file type.
navigator.share() rejects with one of four error types. NotAllowedError means no user activation, a policy block, or a blocked file type. AbortError means the user dismissed the sheet or no share target exists. TypeError means the data failed validation. DataError means starting the target or transmitting the data failed. InvalidStateError appears when the document is not fully active or a previous share is still pending.