janus_popup_getSelectedText.js

// Inject _getSelectedTextFromTab into current page and 
// populate the textarea for user input in the popup with the selected text
function getSelectedText() {
    // Get information about the currently active tab
    chrome.tabs.query({ active: true, currentWindow: true }, function (tabs) {
        let tab = tabs[0];
      
        // Inject JavaScript into the active tab to get the text selected by the user
        chrome.scripting.executeScript(
            {
                target: { tabId: tab.id },          // Specify a target to inject JavaScript
                function: _getSelectedTextFromTab,  // Function to be injected into the target
            },
            ([res]) => {
                // If selection is not empty, populate the input textarea
                if (res["result"] !== "") {
                    document.getElementById("input_text").value = res["result"];
                }
            }
        );
    });
};


// Get the selected text from the current page
function _getSelectedTextFromTab() {
    var selection = window.getSelection().toString();
    return selection;
}


// Trigger the injection of script to get user selected text and 
// populate the input textarea whenever the DOM content is loaded
// (without waiting for images and stylesheets to finish loading)
document.addEventListener("DOMContentLoaded", getSelectedText);