background.js

// import {THEMES, add_contextual_menu} from 'lib';

var script_to_call = {file:'anchors-reveal.js'};
var menu_id = 'anchors-reveal';

var THEMES = {
    'ClassicalYellow' : {
        background : 'yellow',
        color : 'black'
    },
    'LightBlue'  : {
        background : '#aaf',
        color : 'black'
    },
    'WhitePaper' : {
        background : 'white',
        color : 'black'
    },
    'GothicAddict' : {
        background : 'black',
        color : 'white'
    },
};

function add_contextual_menu() {
    browser.contextMenus.create({
      id: menu_id,
      title: browser.i18n.getMessage('buttonDescription'),
      icons: {
        '16': "data/icon-16.png",
        '32': "data/icon-32.png"
      }
    });

    browser.contextMenus.onClicked.addListener(function(info, tab) {
      if (info.menuItemId === menu_id) {
        browser.tabs.executeScript(script_to_call);
      }
    });
};

// end import

function instantiate_contextual_menu(result) {
    if (result.menu) {
        add_contextual_menu();
    } else {
        try {
            browser.contextMenus.remove(menu_id);
        }  catch (e) {

        }
    }
}

//The following was modified from http://stackoverflow.com/a/40517692/3773011 Copied by the author of the post.
function handleExecuteScriptAndInsertCSSErrors(tabId){
    if (chrome.runtime.lastError){
        let isFirefox = !!window.InstallTrigger;

        let message = chrome.runtime.lastError.message ? chrome.runtime.lastError : chrome.runtime.lastError.message;

        window.console.error(message);
    }
}

function oops(e) {
    window.console.error(e);
}

let getting = browser.storage.local.get('menu');
getting.then(instantiate_contextual_menu, oops);

chrome.browserAction.onClicked.addListener(function(tab){
    chrome.tabs.executeScript(tab.id, script_to_call, handleExecuteScriptAndInsertCSSErrors);
});