devtools.js

// Can use
// chrome.devtools.*
// chrome.extension.*

// most likely this will run when devtools opens
var backgroundPageConnection = chrome.runtime.connect({
    name: "devtools-page"
});



(function createChannel() {
    //Create a port with background page for continous message communication
    var port = chrome.extension.connect({
        name: "Another Communication" //Given a Name
    });

    // Listen to messages from the background page
    port.onMessage.addListener(function (message) {
        if (message.action === "downloadHARlog") {
            chrome.devtools.network.getHAR(
                (harLog) => {
                    let updatedHarLog = {};

                    // this makes it readable by Chrome Dev Tools
                    updatedHarLog.log = harLog;

                    let harBLOB = new Blob([JSON.stringify(updatedHarLog)]);

                    let url = URL.createObjectURL(harBLOB);

                    chrome.downloads.download({
                        url: url
                    });
                    
                }
            );
        }
    });

}());