jQuery的函数$(function())在$(function())多次调用时的执行顺序

Question

代码如下：

$(window.document).ready(function () {
    window.alert('alert 1');
});

$(function () {
    window.alert('alert 2');
});

$(function () {
   window.alert('alert 3');
});

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo2</title>
    <script src="jquery-3.1.1.js"></script>
    <script src="demo2.js"></script>
</head>
<body>

</body>
</html>

当我执行上面的代码时，页面的提示顺序有时是：警报 1、警报 2、警报 3，有时是：警报 1、警报 3、警报 2。谁能告诉我为什么？

Answer 1

在第 3930 到 3947 jQuery 行，版本 3.1.1 处理 .ready() 在 document 已经加载后被调用。在第 3938 行 jQuery.ready 在 setTimeout 内部被调用，没有设置带有附加注释

的持续时间

// Handle it asynchronously to allow scripts the opportunity to delay ready

这将解释如何在 window.alert('alert 2')

之前调用 window.alert('alert 3')

// Catch cases where $(document).ready() is called
// after the browser event has already occurred.
// Support: IE <=9 - 10 only
// Older IE sometimes signals "interactive" too soon
if ( document.readyState === "complete" ||
    ( document.readyState !== "loading" && !document.documentElement.doScroll ) ) {

    // Handle it asynchronously to allow scripts the opportunity to delay ready
    window.setTimeout( jQuery.ready ); // Line 3938

} else {

    // Use the handy event callback
    document.addEventListener( "DOMContentLoaded", completed );

    // A fallback to window.onload, that will always work
    window.addEventListener( "load", completed );
}

以下 stacksnippet 应该重现 OP

描述的结果

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>Demo2</title>
  <script src="https://code.jquery.com/jquery-3.1.1.js"></script>
  <script>
    $(window.document).ready(function() {
      window.alert('alert 1');
    });

    $(function() {
      window.alert('alert 2');
    });

    $(function() {
      window.alert('alert 3');
    });
  </script>
</head>

<body>

</body>

</html>

另请参阅第 3924 行的 completed 函数

// The ready event handler and self cleanup method
function completed() {
    document.removeEventListener( "DOMContentLoaded", completed );
    window.removeEventListener( "load", completed );
    jQuery.ready();
}

参见版本 1

的 plnkr http://plnkr.co/edit/C0leBhYJq8CMh7WqndzH?p=preview

编辑、更新

为了确保函数在 .ready() 处的执行顺序，您可以 return 来自函数调用的承诺，在单个 .ready() 调用中使用 .then() 来调用函数全局定义或之前在 .ready() 处理程序中定义。

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>Demo2</title>
  <script src="https://code.jquery.com/jquery-3.1.1.js"></script>
  <script>
    function ready1(wait, index) {
      // do stuff
      return new Promise(resolve => {
          setTimeout(() => {
            window.alert('alert ' + index);
            resolve(index)
          }, wait)
        })
        .then((i) => console.log(i))
    }

    function ready2(wait, index) {
      // do stuff
      return new Promise(resolve => {
          setTimeout(() => {
            window.alert('alert ' + index);
            resolve(index)
          }, wait)
        })
        .then((i) => console.log(i))
    }

    function ready3(wait, index) {
      // do stuff
      return new Promise(resolve => {
          setTimeout(() => {
            window.alert('alert' + index);
            resolve(index)
          }, wait)
        })
        .then((i) => console.log(i))
    }
    $().ready(function() {
      ready1(3000, 0) 
      .then(function() {
        return ready2(1500, 1) 
      })
      .then(function() {
        return ready3(750, 2) 
      });
    })
  </script>
</head>

</html>

jQuery的函数$(function())在$(function())多次调用时的执行顺序

jQuery's function $(function())’s execute order when the $(function()) called more one times

javascript

jquery

jquery-3