Software Development

Detect the Content Type in the Clipboard


A user’s clipboard is a “catch all” between the operating system and the apps employed on it. When you use a web browser, you can highlight text or right-click an image and select “Copy Image”. That made me think about how developers can detect what is in the clipboard.

You can retrieve the contents of the user’s clipboard using the navigator.clipboard API. This API requires user permission as the clipboard could contain sensitive data. You can employ the following JavaScript to get permission to use the clipboard API:

const result = await navigator.permissions.query({name: "clipboard-write"});
if (result.state === "granted" || result.state === "prompt") {
  // Clipboard permissions available
}

With clipboard permissions granted, you query the clipboard to get a ClipboardItem instance with details of what’s been copied:

const [item] = await navigator.clipboard.read();

// When text is copied to clipboard....
item.types // ["text/plain"]

// When an image is copied from a website...
item.types // ["text/html", "image/png"]

Once you know the contents and the MIME type, you can get the text in clipboard with readText():

const content = await navigator.clipboard.readText();

In the case of an image, if you have the MIME type and content available, you can use <img> with a data URI for display. Knowing the contents of a user’s clipboard can be helpful when presenting exactly what they’ve copied!

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