jQuery加载和更改[重复]

This question already has an answer here:

Jquery click event not firing on the element created dynamically using jquery 3 answers

I have a 'test.html' and a 'test.php' files.

The 'test.html':

<html>
  <head>
    <script type="text/javascript" src="/js/jquery-1.8.2.js"></script>
  </head>
  <body>
    <p>Hello</p>
  </body>
</html>

<script type="text/javascript">
  $(function() {
    $("p").on('click', function() {
      $(this).load("test.php");
      $(this).off();
    });
  });
</script>

<script type="text/javascript">
  $(function() {
    $("#sel_1").on('change', function() {
      alert("SELECT changed!");
    });
  });
</script>

And the 'test.php':

<?php
  echo "<select id='sel_1'>";
  echo "<option>one</option>";
  echo "<option>two</option>";
  echo "<option>three</option>";
  echo "</select>";
?>

When i click the 'p' item (Hello), then the jQuery load a new content into 'p'.

But when i change a select item, I would like to see the alert messages, but it will not appear. How can I solve this?

</div>

This should work:

<script type="text/javascript">
  $(function() {
    $('body').on('change', "#sel_1", function() {
      alert("SELECT changed!");
    });
  });
</script>

As others mentionned, you need to use event delegation.

Here is a small example:

html:

<div>
    Hello
</div>

<button> Add Content </button>

javascript:

$(function () {
    $("button")
        .on('click', function () {
            $("div")
                .append(getSelect());
        });

    $("div")
        .on('change', '.mySelects', function () {
            alert('select changed!');
        });
});

function getSelect() {
    return $("<select></select>")
        .addClass("mySelects")
        .append($("<option></option>")
            .html("abc")
            .val("1"))
        .append($("<option></option>")
            .html("def")
            .val("2"));
}