使用 fetch 代替 ajax（在不支持的浏览器上使用 XHR）； This kind of functionality was previously achieved using XMLHttpRequest.

原生 JS Ajax,GET和POST 请求实例代码_javascript技巧_脚本之家 https://www.jb51.net/article/86157.htm

更新时间：2016年06月08日 10:18:06

javascript/js的ajax的GET请求代码如下所示：

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<script type="text/javascript"> /* 创建 XMLHttpRequest 对象 */ var xmlHttp; function GetXmlHttpObject(){ 　　if (window.XMLHttpRequest){ 　　　　// code for IE7+, Firefox, Chrome, Opera, Safari 　　　　xmlhttp=new XMLHttpRequest(); 　　}else{// code for IE6, IE5 　　　　xmlhttp=new ActiveXObject("Microsoft.XMLHTTP"); 　　} 　　return xmlhttp; } // -----------ajax方法-----------// function getLabelsGet(){ 　　xmlHttp=GetXmlHttpObject(); 　　if (xmlHttp==null){ 　　　　alert('您的浏览器不支持AJAX！'); 　　　　return; 　　} 　　var id = document.getElementById('id').value; 　　var url="http://www.Leefrom.com?id="+id+"&t/"+Math.random(); 　　xmlHttp.open("GET",url,true); 　　xmlHttp.onreadystatechange=favorOK;//发送事件后，收到信息了调用函数 　　xmlHttp.send(); } function getOkGet(){ 　　if(xmlHttp.readyState==1||xmlHttp.readyState==2||xmlHttp.readyState==3){ 　　　　// 本地提示：加载中 　　} 　　if (xmlHttp.readyState==4 && xmlHttp.status==200){ 　　　　var d= xmlHttp.responseText; 　　　　// 处理返回结果 　　} } </script>

javascript/js的ajax的POST请求：

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<script type="text/javascript"> /* 创建 XMLHttpRequest 对象 */ var xmlHttp; function GetXmlHttpObject(){ if (window.XMLHttpRequest){ // code for IE7+, Firefox, Chrome, Opera, Safari xmlhttp=new XMLHttpRequest(); }else{// code for IE6, IE5 xmlhttp=new ActiveXObject("Microsoft.XMLHTTP"); } return xmlhttp; } // -----------ajax方法-----------// function getLabelsPost(){ xmlHttp=GetXmlHttpObject(); if (xmlHttp==null){ alert('您的浏览器不支持AJAX！'); return; } var url="http://www.lifefrom.com/t/"+Math.random(); xmlhttp.open("POST",url,true); xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded"); xmlhttp.send(); xmlHttp.onreadystatechange=getLabelsOK;//发送事件后，收到信息了调用函数 } function getOkPost(){ if(xmlHttp.readyState==1||xmlHttp.readyState==2||xmlHttp.readyState==3){ // 本地提示：加载中/处理中 } if (xmlHttp.readyState==4 && xmlHttp.status==200){ var d=xmlHttp.responseText; // 返回值 // 处理返回值 } } </script>

注意：XMLHttpRequest 是 AJAX 的基础，在创建 XMLHttpRequest 对象时，必须与你写的ajax方法在同一个‘<script></script>'标签中！否则ajax请求会出错，并无法返回数据。 javascript/js的ajax的POST/GET请求。

• 使用 fetch 代替 ajax（在不支持的浏览器上使用 XHR）；

Using Fetch - Web APIs | MDN https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch

The Fetch API provides a JavaScript interface for accessing and manipulating parts of the HTTP pipeline, such as requests and responses. It also provides a global fetch() method that provides an easy, logical way to fetch resources asynchronously across the network.

This kind of functionality was previously achieved using XMLHttpRequest. Fetch provides a better alternative that can be easily used by other technologies such as Service Workers. Fetch also provides a single logical place to define other HTTP-related concepts such as CORS and extensions to HTTP.

The fetch specification differs from jQuery.ajax() in two main ways:

• The Promise returned from fetch() won’t reject on HTTP error status even if the response is an HTTP 404 or 500. Instead, it will resolve normally (with ok status set to false), and it will only reject on network failure or if anything prevented the request from completing.
• By default, fetch won't send or receive any cookies from the server, resulting in unauthenticated requests if the site relies on maintaining a user session (to send cookies, the credentials init option must be set).
  Since Aug 25, 2017. The spec changed the default credentials policy to same-origin. Firefox changed since 61.0b13.

A basic fetch request is really simple to set up. Have a look at the following code:

fetch('http://example.com/movies.json')
  .then(function(response) {
    return response.json();
  })
  .then(function(myJson) {
    console.log(JSON.stringify(myJson));
  });

Here we are fetching a JSON file across the network and print it to the console. The simplest use of fetch() takes one argument — the path to the resource you want to fetch — and returns a promise containing the response (a Response object).

This is just an HTTP response of course, not the actual JSON. To extract the JSON body content from the response, we use the json() method (defined on the Body mixin, which is implemented by both the Request and Response objects.)

Note: The Body mixin also has similar methods to extract other types of body content; see the Body section for more.

Fetch requests are controlled by the connect-src directive of Content Security Policy rather than the directive of the resources it's retrieving.

Supplying request optionsSection

The fetch() method can optionally accept a second parameter, an init object that allows you to control a number of different settings:

See fetch() for the full options available, and more details.

// Example POST method implementation:

postData(`http://example.com/answer`, {answer: 42})
  .then(data => console.log(JSON.stringify(data))) // JSON-string from `response.json()` call
  .catch(error => console.error(error));

function postData(url = ``, data = {}) {
  // Default options are marked with *
    return fetch(url, {
        method: "POST", // *GET, POST, PUT, DELETE, etc.
        mode: "cors", // no-cors, cors, *same-origin
        cache: "no-cache", // *default, no-cache, reload, force-cache, only-if-cached
        credentials: "same-origin", // include, *same-origin, omit
        headers: {
            "Content-Type": "application/json; charset=utf-8",
            // "Content-Type": "application/x-www-form-urlencoded",
        },
        redirect: "follow", // manual, *follow, error
        referrer: "no-referrer", // no-referrer, *client
        body: JSON.stringify(data), // body data type must match "Content-Type" header
    })
    .then(response => response.json()); // parses response to JSON
}

Sending a request with credentials includedSection

To cause browsers to send a request with credentials included, even for a cross-origin call, add credentials: 'include' to the init object you pass to the fetch() method.

fetch('https://example.com', {
  credentials: 'include'
})

If you only want to send credentials if the request URL is on the same origin as the calling script, add credentials: 'same-origin'.

// The calling script is on the origin 'https://example.com'

fetch('https://example.com', {
  credentials: 'same-origin'
})

To instead ensure browsers don’t include credentials in the request, use credentials: 'omit'.

fetch('https://example.com', {
  credentials: 'omit'
})

Uploading JSON dataSection

Use fetch() to POST JSON-encoded data.

var url = 'https://example.com/profile';
var data = {username: 'example'};

fetch(url, {
  method: 'POST', // or 'PUT'
  body: JSON.stringify(data), // data can be `string` or {object}!
  headers:{
    'Content-Type': 'application/json'
  }
}).then(res => res.json())
.then(response => console.log('Success:', JSON.stringify(response)))
.catch(error => console.error('Error:', error));

Uploading a fileSection

Files can be uploaded using an HTML <input type="file" /> input element, FormData()and fetch().

var formData = new FormData();
var fileField = document.querySelector("input[type='file']");

formData.append('username', 'abc123');
formData.append('avatar', fileField.files[0]);

fetch('https://example.com/profile/avatar', {
  method: 'PUT',
  body: formData
})
.then(response => response.json())
.catch(error => console.error('Error:', error))
.then(response => console.log('Success:', JSON.stringify(response)));

Uploading multiple filesSection

Files can be uploaded using an HTML <input type="file" /> input element, FormData()and fetch().

var formData = new FormData();
var photos = document.querySelector("input[type='file'][multiple]");

formData.append('title', 'My Vegas Vacation');
formData.append('photos', photos.files);

fetch('https://example.com/posts', {
  method: 'POST',
  body: formData
})
.then(response => response.json())
.then(response => console.log('Success:', JSON.stringify(response)))
.catch(error => console.error('Error:', error));

Checking that the fetch was successfulSection

A fetch() promise will reject with a TypeError when a network error is encountered or CORS is misconfigured on the server side, although this usually means permission issues or similar — a 404 does not constitute a network error, for example. An accurate check for a successful fetch() would include checking that the promise resolved, then checking that the Response.ok property has a value of true. The code would look something like this:

fetch('flowers.jpg').then(function(response) {
  if(response.ok) {
    return response.blob();
  }
  throw new Error('Network response was not ok.');
}).then(function(myBlob) {
  var objectURL = URL.createObjectURL(myBlob);
  myImage.src = objectURL;
}).catch(function(error) {
  console.log('There has been a problem with your fetch operation: ', error.message);
});

Supplying your own request objectSection

Instead of passing a path to the resource you want to request into the fetch() call, you can create a request object using the Request() constructor, and pass that in as a fetch()method argument:

var myHeaders = new Headers();

var myInit = { method: 'GET',
               headers: myHeaders,
               mode: 'cors',
               cache: 'default' };

var myRequest = new Request('flowers.jpg', myInit);

fetch(myRequest).then(function(response) {
  return response.blob();
}).then(function(myBlob) {
  var objectURL = URL.createObjectURL(myBlob);
  myImage.src = objectURL;
});

Request() accepts exactly the same parameters as the fetch() method. You can even pass in an existing request object to create a copy of it:

var anotherRequest = new Request(myRequest, myInit);

This is pretty useful, as request and response bodies are one use only. Making a copy like this allows you to make use of the request/response again, while varying the init options if desired. The copy must be made before the body is read, and reading the body in the copy will also mark it as read in the original request.

Note: There is also a clone() method that creates a copy. Both methods of creating a copy will fail if the body of the original request or response has already been read, but reading the body of a cloned response or request will not cause it to be marked as read in the original.

HeadersSection

The Headers interface allows you to create your own headers object via the Headers()constructor. A headers object is a simple multi-map of names to values:

var content = "Hello World";
var myHeaders = new Headers();
myHeaders.append("Content-Type", "text/plain");
myHeaders.append("Content-Length", content.length.toString());
myHeaders.append("X-Custom-Header", "ProcessThisImmediately");

The same can be achieved by passing an array of arrays or an object literal to the constructor:

myHeaders = new Headers({
  "Content-Type": "text/plain",
  "Content-Length": content.length.toString(),
  "X-Custom-Header": "ProcessThisImmediately",
});

The contents can be queried and retrieved:

console.log(myHeaders.has("Content-Type")); // true
console.log(myHeaders.has("Set-Cookie")); // false
myHeaders.set("Content-Type", "text/html");
myHeaders.append("X-Custom-Header", "AnotherValue");

console.log(myHeaders.get("Content-Length")); // 11
console.log(myHeaders.get("X-Custom-Header")); // ["ProcessThisImmediately", "AnotherValue"]

myHeaders.delete("X-Custom-Header");
console.log(myHeaders.get("X-Custom-Header")); // [ ]

Some of these operations are only useful in ServiceWorkers, but they provide a much nicer API for manipulating headers.

All of the Headers methods throw a TypeError if a header name is used that is not a valid HTTP Header name. The mutation operations will throw a TypeError if there is an immutable guard (see below). Otherwise they fail silently. For example:

var myResponse = Response.error();
try {
  myResponse.headers.set("Origin", "http://mybank.com");
} catch(e) {
  console.log("Cannot pretend to be a bank!");
}

A good use case for headers is checking whether the content type is correct before you process it further. For example:

fetch(myRequest).then(function(response) {
    var contentType = response.headers.get("content-type");
    if(contentType && contentType.includes("application/json")) {
      return response.json();
    }
    throw new TypeError("Oops, we haven't got JSON!");
  })
  .then(function(json) { /* process your JSON further */ })
  .catch(function(error) { console.log(error); });

GuardSection

Since headers can be sent in requests and received in responses, and have various limitations about what information can and should be mutable, headers objects have a guard property. This is not exposed to the Web, but it affects which mutation operations are allowed on the headers object.

Possible guard values are:

• none: default.
• request: guard for a headers object obtained from a request (Request.headers).
• request-no-cors: guard for a headers object obtained from a request created with Request.mode no-cors.
• response: guard for a Headers obtained from a response (Response.headers).
• immutable: Mostly used for ServiceWorkers; renders a headers object read-only.

Note: You may not append or set a request guarded Headers’ Content-Length header. Similarly, inserting Set-Cookie into a response header is not allowed: ServiceWorkers are not allowed to set cookies via synthesized responses.

Response objectsSection

As you have seen above, Response instances are returned when fetch() promises are resolved.

The most common response properties you'll use are:

• Response.status — An integer (default value 200) containing the response status code.
• Response.statusText — A string (default value "OK"), which corresponds to the HTTP status code message.
• Response.ok — seen in use above, this is a shorthand for checking that status is in the range 200-299 inclusive. This returns a Boolean.

They can also be created programmatically via JavaScript, but this is only really useful in ServiceWorkers, when you are providing a custom response to a received request using a respondWith() method:

var myBody = new Blob();

addEventListener('fetch', function(event) { // ServiceWorker intercepting a fetch
  event.respondWith(
    new Response(myBody, {
      headers: { "Content-Type" : "text/plain" }
    })
  );
});

The Response() constructor takes two optional arguments — a body for the response, and an init object (similar to the one that Request() accepts.)

Note: The static method error() simply returns an error response. Similarly, redirect() returns a response resulting in a redirect to a specified URL. These are also only relevant to Service Workers.

BodySection

Both requests and responses may contain body data. A body is an instance of any of the following types:

• ArrayBuffer
• ArrayBufferView (Uint8Array and friends)
• Blob/File
• string
• URLSearchParams
• FormData

The Body mixin defines the following methods to extract a body (implemented by both Request and Response). These all return a promise that is eventually resolved with the actual content.

• arrayBuffer()
• blob()
• json()
• text()
• formData()

This makes usage of non-textual data much easier than it was with XHR.

Request bodies can be set by passing body parameters:

var form = new FormData(document.getElementById('login-form'));
fetch("/login", {
  method: "POST",
  body: form
});

Both request and response (and by extension the fetch() function), will try to intelligently determine the content type. A request will also automatically set a Content-Type header if none is set in the dictionary.

Feature detectionSection

Fetch API support can be detected by checking for the existence of Headers, Request, Response or fetch() on the Window or Worker scope. For example:

if (self.fetch) {
    // run my fetch request here
} else {
    // do something with XMLHttpRequest?
}

PolyfillSection

To use Fetch in unsupported browsers, there is a Fetch Polyfill available that recreates the functionality for non-supporting browsers.