xhr.onreadystatechange = function() { if (xhr.readyState === 4 && xhr.status === 200)什么意思
时间: 2023-10-08 16:04:56 浏览: 35
This code snippet sets a callback function for the `readystatechange` event of an `XMLHttpRequest` object (`xhr`). The `readystatechange` event is fired several times as the request progresses through different states, and the callback function is called each time to handle the response data.
The code checks if the `readyState` property of the `xhr` object is equal to 4, which means that the request has completed and the response data is available. If the condition is true, the callback function can access the response data using the `xhr.responseText` property and perform any necessary processing.
相关问题
xhr.onreadystatechange = function() { if (xhr.readyState === 4 && xhr.status === 200)
This is an incomplete line of JavaScript code. It seems that the code block is checking for the readyState of an XMLHttpRequest object (represented by the variable 'xhr'). The number 4 represents the value of the readyState property when the request has been completed and the response is ready. However, the rest of the code is missing, so it's unclear what action is being taken based on the readyState value.
xhr.onreadystatechange = function () { if (xhr.readyState === 4 && xhr.status === 200) { // 处理响应 } };这个回调函数要写什么,给个案例,不要写console.log
好的,下面是一个例子:
```javascript
xhr.onreadystatechange = function () {
if (xhr.readyState === 4 && xhr.status === 200) {
const response = JSON.parse(xhr.responseText);
const result = document.getElementById("result");
result.innerHTML = response.message;
}
};
```
在这个例子中,当 XMLHttpRequest 对象的 readyState 状态变为 4,也就是完成状态,而且 status 状态变为 200,也就是成功状态时,会执行这个回调函数中的代码。这里的代码将响应文本解析为 JSON 对象,并将其中的 message 属性的值赋给一个 id 为 result 的 HTML 元素的 innerHTML 属性,从而在页面上显示这个值。这个例子中的代码可以根据实际需要进行修改,以实现不同的响应处理逻辑。