When sending an Ajax request, if there is no corresponding file content in the requested file, or if the path is wrong, the page will report an error. Here’s a brief introduction, such as how to avoid page error reporting, or page compatibility

xhr.onreadystatechange = function() {
  
  if(xhr.readyState == 4) {
    //Verify that the file is available, using status to determine the status
    if(xhr.status >= 200 && xhr.status < 300 || xhr.status == 304) {
      box.innerHTML = xhr.responseText;
    }else {
      // Error page, server error or not found error
      console.error("Error Request")
    }
  }
}

This page will not appear the following error problem

The error will be output on the console