# Iframe API

This page assumes you've added an iframe to your HTML as described in the embedding example and assigned it to a variable called iframeElement. For example:

const iframeElement = document.getElementById("browserboard");

Iframes allow two-way communication. To get a message in, you use the postMessage (opens new window) method on your iframe element. To get messages out, you listen to the "message" (opens new window) event on window. Browserboard uses both of these things to communicate with your code in the web browser.

The "in" and "out" message objects both use "action" as an object key representing what should be done. You can "send a message" to Browserboard or "receive a message" from Browserboard, and the "action" tells us what to do with the message.

# Configuring the interface using the URL hash

You can configure a few of Browserboard's features using the URL hash, appended to the URL you pass to the iframe. Here is a comprehensive example:

<iframe
  src="https://browserboard.com/whiteboard/$board_id?access_key=$access_key#colors=%23f00,%2300f&strokeWidths=2,3,4,20&defaultLineCap=square&tools=line,select&isZoomAllowed=false"
  ...
>
</iframe>

Append this to the URL you put in the iframe.

  • colors: Comma-separated list of colors. Make sure to escape # characters as %23. Translucent colors defined with rgba are allowed.
  • strokeWidths: Comma-separated list of stroke widths.
  • defaultLineCap: round, butt, or square. Google "MDN linecap" for details. Browserboard's default is round.
  • tools: Comma-separated list of tools to display. Possible values are:
    • arrow
    • line
    • pan
    • pen
    • marker
    • rect
    • diamond
    • ellipse
    • select
    • eraser
    • text
    • sticky
    • imageLibrary
    • imageUpload
  • isZoomAllowed: If false, zoom controls are disabled.

# Sending messages

Telling Browserboard to do things always looks like this:

iframeElement.contentWindow.postMessage(
  // what to send
  { action: "actionName", ...otherArguments },
  // tell the browser who we expect the iframe to be
  "https://browserboard.com"
);

You might want to condense this down with a helper function:

function sendBrowserboardMessage(message) {
  iframeElement.contentWindow.postMessage(message, "https://browserboard.com");
}

# Receiving messages

Subscribe to the "message" event on window, like this:

window.addEventListener("message", (e) => {
  switch (e.data.action) {
    case "actionName":
      break; /* handle the action */
    /* the rest of this file will explain what actions exist and how to handle them. */
  }
});

# Downloading images

To convert the whiteboard to a PNG and get a copy of it, send this message:

{ "action": "downloadImage" }

Then, wait for these messages:

{
    // This action may fire if the image takes a long time to render.
    "action": "updateDownloadImageProgress",
    "progress": number, // 0-1
}
{
    "action": "downloadImageComplete",
    "url": string, // this is a data URL
}

# Inserting images and PDFs

To insert an image into the board, use the insertImage message. The value of url must point to an image that already exists on the web.

sendBrowserboardMessage({
  action: "insertImage",
  url: "https://the/image/url",
});

To insert a PDF, use the insertPDF message. Browserboard will prompt the user for a page range to insert.

sendBrowserboardMessage({ action: "insertPDF", url: "https://the/pdf/url" });

# Customizing colors

To replace the default colors with multiple groups of colors, use the setCustomColors message.

sendBrowserboardMessage({
  action: "setCustomColors",
  colors: [
    ["Group 1", ["red", "green"]],
    ["Group 2", ["blue", "purple"]],
  ],
});