js中onclic怎么用

<button onclick="alert('Hello, World!');">Click Me</button>

<button id="myButton">Click Me</button>

<script>
  document.getElementById('myButton').onclick = function() {
    alert('Hello, World!');
  };
</script>

<button id="myButton">Click Me</button>

<script>
  document.getElementById('myButton').addEventListener('click', function() {
    alert('Hello, World!');
  });
</script>

window.onload = function() {
  document.getElementById('myButton').addEventListener('click', function() {
    alert('Hello, World!');
  });
};

function addEvent(element, event, handler) {
  if (element.addEventListener) {
    element.addEventListener(event, handler, false);
  } else if (element.attachEvent) {
    element.attachEvent('on' + event, handler);
  } else {
    element['on' + event] = handler;
  }
}

addEvent(document.getElementById('myButton'), 'click', function() {
  alert('Hello, World!');
});