Chrome Extension Content Script Access Global Variables & manipulate DOM

ChromeExtensionContentScript.js

function executeOnPageSpace(code){

    // create a script tag
    var script = document.createElement('script')
    script.id = 'tmpScript'
    // place the code inside the script. later replace it with execution result.
    script.textContent = 
    'document.getElementById("tmpScript").textContent = JSON.stringify(' + code + ')'
    // attach the script to page
    document.documentElement.appendChild(script)
    // collect execution results
    let result = document.getElementById("tmpScript").textContent
    // remove script from page
    script.remove()
    return JSON.parse(result)
  
 }
 
let tabAddress = executeOnPageSpace('window.location.href')
alert('You are on: ' + tabAddress + '\nLets go somewhere else!')
executeOnPageSpace('window.location.href = "http://github.com"')