if (xhr.readyState === 4 && xhr.status === 200) 这个可以不写吗

在使用Ajax时，通常会使用`xhr.readyState`和`xhr.status`来判断请求是否完成并且服务器返回的状态码是否为200（即成功）。这是基本的错误处理和状态检查步骤，可以帮助你确保获取到正确的响应数据并进行相应的处理。

但是，如果你不写这个条件判断，那么无法准确地确定请求是否成功完成。这意味着无论请求是否成功，都会执行相应的处理代码。这可能会导致程序在出现错误或服务器返回其他状态码时出现异常行为。

因此，为了确保代码的正确性和健壮性，建议在Ajax请求中始终包含这个条件判断。通过检查`xhr.readyState`是否为4（表示请求已完成）和`xhr.status`是否为200（表示成功），你可以确保只有在请求成功完成且服务器返回状态码为200时才执行后续的处理代码。

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)什么意思

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.