现代、干净、简洁

fetch('https://baconipsum.com/api/?type=1')

让url = 'https://baconipsum.com/api/?type=all-meat&paras=1&start-with-lorem=2'; //只发送GET请求而不等待响应 fetch (url); //使用then来等待结果 获取(url)。然后(r = > r.json()。then(j=> console.log('\nREQUEST 2'，j))); //或async/await (异步()= > console.log('\nREQUEST 3'， await(await fetch(url)).json()) ) (); 打开Chrome控制台网络选项卡查看请求

原型让它变得非常简单

new Ajax.Request( '/myurl', {
  method:  'get',
  parameters:  { 'param1': 'value1'},
  onSuccess:  function(response){
    alert(response.responseText);
  },
  onFailure:  function(){
    alert('ERROR');
  }
});

下面是直接用JavaScript实现的代码。但是，如前所述，使用JavaScript库会更好。我最喜欢jQuery。

在下面的例子中，调用一个ASPX页面(作为穷人的REST服务)来返回一个JavaScript JSON对象。

var xmlHttp = null;

function GetCustomerInfo()
{
    var CustomerNumber = document.getElementById( "TextBoxCustomerNumber" ).value;
    var Url = "GetCustomerInfoAsJson.aspx?number=" + CustomerNumber;

    xmlHttp = new XMLHttpRequest(); 
    xmlHttp.onreadystatechange = ProcessRequest;
    xmlHttp.open( "GET", Url, true );
    xmlHttp.send( null );
}

function ProcessRequest() 
{
    if ( xmlHttp.readyState == 4 && xmlHttp.status == 200 ) 
    {
        if ( xmlHttp.responseText == "Not found" ) 
        {
            document.getElementById( "TextBoxCustomerName"    ).value = "Not found";
            document.getElementById( "TextBoxCustomerAddress" ).value = "";
        }
        else
        {
            var info = eval ( "(" + xmlHttp.responseText + ")" );

            // No parsing necessary with JSON!        
            document.getElementById( "TextBoxCustomerName"    ).value = info.jsonData[ 0 ].cmname;
            document.getElementById( "TextBoxCustomerAddress" ).value = info.jsonData[ 0 ].cmaddr1;
        }                    
    }
}

浏览器(和Dashcode)提供了一个XMLHttpRequest对象，可用于从JavaScript发出HTTP请求:

function httpGet(theUrl)
{
    var xmlHttp = new XMLHttpRequest();
    xmlHttp.open( "GET", theUrl, false ); // false for synchronous request
    xmlHttp.send( null );
    return xmlHttp.responseText;
}

然而，不鼓励同步请求，并将生成如下警告:

注意:从Gecko 30.0 (Firefox 30.0 / Thunderbird 30.0 / SeaMonkey 2.27)开始，由于对用户体验的负面影响，主线程上的同步请求已被弃用。

您应该在事件处理程序中发出异步请求并处理响应。

function httpGetAsync(theUrl, callback)
{
    var xmlHttp = new XMLHttpRequest();
    xmlHttp.onreadystatechange = function() { 
        if (xmlHttp.readyState == 4 && xmlHttp.status == 200)
            callback(xmlHttp.responseText);
    }
    xmlHttp.open("GET", theUrl, true); // true for asynchronous 
    xmlHttp.send(null);
}

// Create a request variable and assign a new XMLHttpRequest object to it.
var request = new XMLHttpRequest()

// Open a new connection, using the GET request on the URL endpoint
request.open('GET', 'restUrl', true)

request.onload = function () {
  // Begin accessing JSON data here
}

// Send request
request.send()

在纯javascript和返回一个承诺:

  httpRequest = (url, method = 'GET') => {
    return new Promise((resolve, reject) => {
      const xhr = new XMLHttpRequest();
      xhr.open(method, url);
      xhr.onload = () => {
        if (xhr.status === 200) { resolve(xhr.responseText); }
        else { reject(new Error(xhr.responseText)); }
      };
      xhr.send();
    });
  }