NetflixBackup/extension/src/js/inject.js

/**
 * injectScript - Inject internal script to available access to the `window`
 *
 * @param  {type} file_path Local path of the internal script.
 * @param  {type} tag The tag as string, where the script will be append (default: "body").
 * @see    {@link http://stackoverflow.com/questions/20499994/access-window-variable-from-content-script}
 */
function injectScript(file_path, tag) {
    var node = document.getElementsByTagName(tag)[0];
    var script = document.createElement("script");
    script.setAttribute("type", "text/javascript");
    script.setAttribute("src", file_path);
    node.appendChild(script);
}
function injectData(property, value, tag) {
    var node = document.getElementsByTagName(tag)[0];
    var span = document.createElement("span");
    span.setAttribute("id", `property-${property}`);
    span.setAttribute("data-value", value);
    console.log(property, value, tag, node);
    node.appendChild(span);
}
injectData("extension-id", chrome.runtime.id, "body");
injectScript(chrome.extension.getURL("js/content.js"), "body");