JSOM - SharePoint 2016

// Assuming you have an array of site collection URLs named "siteCollectionUrls"
let siteCollectionUrls = ["site1", "site2", "site3"];

// Function to check user permission in a site collection
function checkUserPermission(url) {
  return new Promise((resolve, reject) => {
    let clientContext = new SP.ClientContext(url);
    let web = clientContext.get_web();
    let currentUser = web.get_currentUser();
    clientContext.load(currentUser);
    clientContext.executeQueryAsync(
      function () {
        // User has permission in this site collection
        resolve(url);
      },
      function (sender, args) {
        // User does not have permission in this site collection
        resolve(null);
      }
    );
  });
}

// Function to collect tasks for the logged-in user in the root site of a site collection
function getTasksInRootSite(url) {
  return new Promise((resolve, reject) => {
    let clientContext = new SP.ClientContext(url);
    let web = clientContext.get_web();
    let currentUser = web.get_currentUser();
    clientContext.load(currentUser);
    let tasksList = web.get_lists().getByTitle("Tasks"); // Replace "Tasks" with your actual task list name
    let query = new SP.CamlQuery();
    query.set_viewXml(
      ``
    );
    let tasks = tasksList.getItems(query);
    clientContext.load(tasks);
    clientContext.executeQueryAsync(
      function () {
        let tasksArray = [];
        let taskEnumerator = tasks.getEnumerator();
        while (taskEnumerator.moveNext()) {
          let task = taskEnumerator.get_current();
          tasksArray.push(task.get_item("Title"));
        }
        resolve(tasksArray);
      },
      function (sender, args) {
        resolve(null);
      }
    );
  });
}

// Function to process the array of site collection URLs
async function processSiteCollections() {
  let tasksPromises = [];
  for (let url of siteCollectionUrls) {
    let permission = await checkUserPermission(url);
    if (permission) {
      let tasks = await getTasksInRootSite(url);
      if (tasks && tasks.length > 0) {
        // Process tasks for this site collection
        console.log("Tasks for", url, ":", tasks);
      } else {
        console.log("No tasks found for", url);
      }
    } else {
      console.log("User does not have permission for", url);
    }
  }
}

// Call the main function to start processing the site collection URLs
processSiteCollections();