原生ajax

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

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>

<body>

</body>
<script>
  //手寫ajax
  let xhr = new XMLHttpRequest;
  xhr.open("POST", "http://jspang.com/DemoApi/oftenGoods.php", true);
  xhr.onreadystatechange = function () {
    if (xhr.readyState == 4 && xhr.status == 200) {
      console.log(xhr.responseText)
    }
  }
  xhr.send()
</script>

</html>

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

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>

<body>

</body>
<script>
  //手寫ajax
  var xhr = new XMLHttpRequest()
  xhr.open('POST', "http://jspang.com/DemoApi/oftenGoods.php", true)
  // false就是等待有返回數據的時候再繼續往下走,尚未獲得數據的時候就會卡在那裏,直到獲取數據爲止。 
  // true就是不等待,直接返回,這就是所謂的異步獲取數據!
  xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");

  xhr.onreadystatechange = function () {
    if (xhr.readyState == 4) {
      if (xhr.status == 200) {
        console.log(xhr.responseText)
      }
    }
  }
  xhr.send()
</script>

</html>
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