remwharead/browser-plugins/webextension/launch.js

var taburl;
var port;

function set_taburl(tabs)       // Set taburl to URL of current tab.
{
    let tab = tabs[0];
    taburl = tab.url;
}

function get_tags()             // get tags from text input.
{
    let tags = document.getElementById("tags").value;
    if (tags != "")
    {
        return "-t " + tags + " ";
    }
    return "";
}

function onResponse(response) {
    console.log("Received: " + response);
    if (response == "Command successful.")
    {
        window.close();
    }
    else
    {
        document.getElementById("error").innerHTML =
            "<strong>" + response +  "</strong>";
    }

}

function onError(error) {
    console.log(`Error: ${error}`);
}

function launch()               // Launch wrapper and send tags + URL to stdin.
{
    var arguments = get_tags() + taburl;
    console.log("Sending:  " + arguments + " to remwharead");
    var sending = browser.runtime.sendNativeMessage("remwharead", arguments);
    sending.then(onResponse, onError);
}


// Call set_taburl() with current tab.
browser.tabs.query({currentWindow: true, active: true}).then(set_taburl);

button.addEventListener("click", launch); // Call send() if submit is clicked.

// Click button if enter is hit in text input.
document.querySelector("#tags").addEventListener(
    "keyup", event =>
        {
            if(event.key !== "Enter")
            {
                return;
            }
            document.querySelector("#button").click();
            event.preventDefault();
        });