background.html

<script>
    // Array to hold callback functions
    var callbacks = []; 

    // This function is called onload in the popup code
    function getPageInfo(callback) 
    { 
        // Add the callback to the queue
        callbacks.push(callback); 

        // Injects the content script into the current page 
        chrome.tabs.executeScript(null, { file: "scripts/onPage.js" }); 
    }; 

    // Perform the callback when a request is received from the content script
    chrome.extension.onRequest.addListener(function(request) 
    { 
        // Get the first callback in the callbacks array
        // and remove it from the array
        var callback = callbacks.shift();

        // Call the callback function
        callback(request); 
    }); 
</script>