js发起网络请求

JavaScript可以使用XMLHttpRequest对象或Fetch API来发起网络请求。

使用XMLHttpRequest对象：

var request = new XMLHttpRequest();
request.open('GET', 'https://api.example.com/data', true);

request.onload = function() {
  if (request.status >= 200 && request.status < 400) {
    // Success!
    var data = JSON.parse(request.responseText);
    console.log(data);
  } else {
    // We reached our target server, but it returned an error
    console.log('Error: ' + request.status);
  }
};

request.onerror = function() {
  // There was a connection error of some sort
  console.log('Connection Error');
};

request.send();

使用Fetch API：

fetch('https://api.example.com/data')
  .then(function(response) {
    if (response.ok) {
      return response.json();
    } else {
      throw new Error('Network response was not ok');
    }
  })
  .then(function(data) {
    console.log(data);
  })
  .catch(function(error) {
    console.log('Fetch Error:', error);
  });