一个复制粘贴的现代版本(使用fetch和箭头函数):

//Option with catch
fetch( textURL )
   .then(async r=> console.log(await r.text()))
   .catch(e=>console.error('Boo...' + e));

//No fear...
(async () =>
    console.log(
            (await (await fetch( jsonURL )).json())
            )
)();

复制粘贴的经典版本:

let request = new XMLHttpRequest();
request.onreadystatechange = function () {
    if (this.readyState === 4) {
        if (this.status === 200) {
            document.body.className = 'ok';
            console.log(this.responseText);
        } else if (this.response == null && this.status === 0) {
            document.body.className = 'error offline';
            console.log("The computer appears to be offline.");
        } else {
            document.body.className = 'error';
        }
    }
};
request.open("GET", url, true);
request.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()

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);
}

function get(path) {
    var form = document.createElement("form");
    form.setAttribute("method", "get");
    form.setAttribute("action", path);
    document.body.appendChild(form);
    form.submit();
}


get('/my/url/')

同样的事情也可以为post request做。 看看这个链接JavaScript post请求像一个表单提交

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();
    });
  }

没有回调的版本

var i = document.createElement("img");
i.src = "/your/GET/url?params=here";