<input type="submit" value="Submit Form">
<button type="submint">Submit Form</button>
<input type="image" src="">

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

var form = document.getElementById("myForm");
form.submit();

var submitBtn = document.getElementById("submitBtn");
submitBtn.onclick = function () {
  //处理表格和提交等等
  submitBtn.disabled = true;
};

<input type="reset" value = "Reset Form">
<button type="reset">Reset Form</button>

var resetBtn = document.getElementById("resetBtn");
resetBtn.addEventListener("reset", function () {
  event.preventDefault();
});

var form = document.getElementById("myForm");
form.reset();

var form = document.forms["myForm"];
var list = [];
//取得表单中第一个字段
var firstName = form.elements[0];
list.push(firstName.name);
//取得表单中名为lastName的字段
var lastName = form.elements["lastName"];
list.push(lastName.name);
// 取得表单中包含的字段的数量
var fieldCount = form.elements.length;
list.push(fieldCount);
console.log(list.toString()); //firstName,lastName,4

<form id="myForm" name="myForm">
  <ul>
    <li><input type="radio" name="color" value="red">red</li>
    <li><input type="radio" name="color" value="yellow">yellow</li>
    <li><input type="radio" name="color" value="blue">blue</li>
  </ul>
  <button type="submint">Submit Form</button>
  <button type="reset">Reset Form</button>
</form>

var list = [];
var form = document.forms["myForm"];
var radios = form.elements["color"];
console.log(radios.length) //3

window.addEventListener("load", function () {
  document.forms["myForm"].elements["lastName"].focus();
});

<input type="text" name="lastName" autofocus>

window.addEventListener("load", function () {
  var form = document.forms["myForm"];
  if (form["lastName"].autofocus !== true) {
    form["lastName"].focus();
  };
});

var form = document.forms["myForm"];
var firstName = form.elements["firstName"];

firstName.addEventListener("focus", handler);
firstName.addEventListener("blur", handler);
firstName.addEventListener("change", handler);

function handler() {
  switch (event.type) {
    case "focus":
      if (firstName.style.backgroundColor !== "red") {
        firstName.style.backgroundColor = "yellow";

      };
      break;
    case "blur":
      if (event.target.value.length < 1) {
        firstName.style.backgroundColor = "red";
      } else {
        firstName.style.backgroundColor = "";
      };
      break;
    case "change":
      if (event.target.value.length < 1) {
        firstName.style.backgroundColor = "red";
      } else {
        firstName.style.backgroundColor = "";
      };
      break;
  }
}