通过javascript提交HTML表单并防止默认

document.getElementById("myForm").addEventListener("submit", function(event) {
  event.preventDefault();
});

document.getElementById("myForm").addEventListener("submit", function(event) {
  event.preventDefault();
  
  var formData = new FormData(event.target);
  var username = formData.get("username");
  var password = formData.get("password");
  
  // 进一步处理表单数据...
});

document.getElementById("myForm").addEventListener("submit", function(event) {
  event.preventDefault();
  
  var formData = new FormData(event.target);
  var username = formData.get("username");
  var password = formData.get("password");
  
  var xhr = new XMLHttpRequest();
  xhr.open("POST", "/submit", true);
  xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
  xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
      // 请求成功，进一步处理返回结果...
    }
  };
  xhr.send("username=" + encodeURIComponent(username) + "&password=" + encodeURIComponent(password));
});