inject css and js to chrome extension

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}
 * @reference https://gist.github.com/devjin0617/3e8d72d94c1b9e69690717a219644c7a?permalink_comment_id=3766826#gistcomment-3766826
 */
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);
}


injectScript(chrome.runtime.getURL('content.js'), 'body');


// Inject CSS
function injectStyle(file_path, tag) {
    var node = document.getElementsByTagName(tag)[0];
    var style = document.createElement('link');
    style.setAttribute('rel', 'stylesheet');
    style.setAttribute('href', file_path);
    node.appendChild(style);
}


injectStyle(chrome.runtime.getURL('style_dictionary.css'), 'head');