let headElement = document.getElementsByTagName('head')[0];

let idInjection = document.createElement('script');
idInjection.innerHTML = 'let extensionId = "' + chrome.runtime.id + '";';
headElement.appendChild(idInjection);

let scriptInjection = document.createElement('script');
scriptInjection.src = chrome.runtime.getURL('injection.js');
headElement.appendChild(scriptInjection);