对javascript返回的工作原理感到困惑

Question

我正在尝试使用jquery编写以下代码。这从网站读取json并创建一个我想要返回的字符串，但它总是返回“undefined”。我在这里错过了什么？

  function getTenders(wardName){
  output = "";
  $.getJSON('http://192.168.1.105:3000/getTenders.json?name='+wardName, function (obj) {
    //console.log(body); // Print the google web page.
    for(var i=0; i < obj.length; i++){
      var pid = "Project id: " + obj[i].id;
      var status = "Status: " + obj[i].status;
      var title = "Title: " + obj[i].title;
      var cost = "Estimated Cost: Rs " + obj[i].estimated;
      output += pid + "\n" + status + "\n" + title + "\n"  + cost + "\n\n";
    }
    console.log("Output: "+ output) // This prints correct output 
    return output // Returning output here 
  });
}

// But this shows undefined

console.log(printTenders("Somevalue")) // This outputs undefined. How can that happen?