Using WebExtension APIs
Extending the simple example extension to make use of WebExtension APIs.
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Extending the simple example extension to make use of WebExtension APIs.
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In the second part of the Hello World Extension Tutorial, we will add a "Details" button to the message header toolbar. A click on it will show some information about the currently displayed message, which we retrieve using Thunderbird's WebExtension APIs.
message_display_actionSimilar to adding the browser_action in the first part of the Hello World Extension Tutorial, we have to extend the manifest.json to add the message_display_action.:
The HTML file for our popup needs some place-holders, which we can later fill using JavaScript and Thunderbird's WebExtension APIs. We create a messagePopup folder inside the hello-world project folder and place the following popup.html file in the newly created folder:
We place the following popup.css file in the same folder as the popup.html file.
The popup.js file was loaded as a top level ES6 module by specifying type="module" in its script tag. This allows us to use the await keyword directly in file scope code. Otherwise we would need to use an asynchronous wrapper function:
async function load() {
let tabs = await messenger.tabs.query({
active: true,
currentWindow: true,
});
...
}
load();
At this stage we are interested in the subject (line 12) and the author (line 13).
We also want to get the received header from the message. That information is not part of the general MessageHeader object, so we have to request the full message.
This is how our manifest.json should now look like:
Open any message and you will find a "Details" button in the message header toolbar. A click on it will show you the subject, the author and the first found received header of the currently viewed message.
Instead of tables, we use modern CSS styling to format our HTML into a tabular view. The display: grid container defines how our 6 DIV elements inside the container DIV are aligned. Check the or this for more details.
All WebExtension API functions return a instead of an actual value. This aims to simplify the handling of asynchronous functions.
The author of this example prefers over the .then() approach for handling Promises. This allows us to avoid the so called callback-hell of asynchronous functions and instead keep writing sequential code by simply awaiting all the returned Promises.
The provides access to Thunderbird's tabs. We need to get hold of the current active tab to learn which message is displayed there. We use the method to find it in line 3.
The method of the provides access to the currently viewed message in a given tab. It returns a Promise for a object from the with basic information about the message in line 9.
The method requires the messagesRead permission, which needs to be added to the permissions key of our manifest.json file.
The method in line 16 returns a Promise for a object, which relates to messages containing multiple MIME parts. The headers member of the part returned by getFull includes the headers of the message (excluding headers which are part of nested MIME parts available through the parts member).
Let's double-check that we made the and have all the files in the right places:
As described in the , go to the Add-ons Manager to open the Debug Add-on Page and temporarily install the extension.
