Javascript 从 XHR 请求中获取 BLOB 数据

Getting BLOB data from XHR request

提问by Nick Bennet

var xhr = new XMLHttpRequest();
xhr.open('GET', 'http://static.reddit.com/reddit.com.header.png', true);

xhr.responseType = 'arraybuffer';

xhr.onload = function(e) {
  if (this.status == 200) {
    var uInt8Array = new Uint8Array(this.response);
    var byte3 = uInt8Array[4]; 

    var bb = new WebKitBlobBuilder();
    bb.append(xhr.response);
    var blob = bb.getBlob('image/png'); 
    var base64 = window.btoa(blob);
    alert(base64);

  }
};

xhr.send();

Basically, what I am trying to do here is retrieve an image, and convert it to base64.

基本上，我在这里尝试做的是检索图像，并将其转换为 base64。

From reading in the comments here, it states:

从阅读这里的评论来看，它指出：

"Sure. After fetching a resource as an ArrayBuffer, create a blob from it. Once you have that, you could base64 encode the file/blob directly window.btoa()or FileReader.readAsDataURL()."

“当然。在将资源作为 ArrayBuffer 获取后，从中创建一个 blob。一旦有了它，您就可以直接对文件/blob 进行 base64 编码 window.btoa()或FileReader.readAsDataURL().”

However, blobis just [object blob], while I need to get the binary from the image so I can convert it to base64 and display it in a img tag using data.

但是，blob只是[object blob]，而我需要从图像中获取二进制文件，以便我可以将其转换为 base64 并使用 data.img 标签将其显示在 img 标签中。

Anyone know how to achieve this?

有谁知道如何实现这一目标？

Thank you in advance!

先感谢您！

回答by Scott A

Don't use BlobBuilder in Chrome (tested in OSX Chrome, Firefox 12, Safari 6, iOS Chrome, iOS Safari):

不要在 Chrome 中使用 BlobBuilder（在 OSX Chrome、Firefox 12、Safari 6、iOS Chrome、iOS Safari 中测试）：

ex1 : http://jsfiddle.net/malraux/xGUsu/(principle)

ex1：http: //jsfiddle.net/malraux/xGUsu/（原理）

ex2: http://jsfiddle.net/xGUsu/78/(working with full example)

ex2：http: //jsfiddle.net/xGUsu/78/（使用完整示例）

var xhr = new XMLHttpRequest();
xhr.open('GET', 'doodle.png', true);

xhr.responseType = 'arraybuffer';

// Process the response when the request is ready.
xhr.onload = function(e) {
  if (this.status == 200) {
    // Create a binary string from the returned data, then encode it as a data URL.
    var uInt8Array = new Uint8Array(this.response);
    var i = uInt8Array.length;
    var binaryString = new Array(i);
    while (i--)
    {
      binaryString[i] = String.fromCharCode(uInt8Array[i]);
    }
    var data = binaryString.join('');

    var base64 = window.btoa(data);

    document.getElementById("myImage").src="data:image/png;base64," + base64;
  }
};

xhr.send();

Note: This code is over 7 years old at this point.While it should still function in most browsers, here's an updated version based on a suggestion by @TypeError that will only work in more modern browsers with the possible exception of iOS Safari(which may or may not support responseType = 'blob'- make sure to test!):

注意：此时此代码已超过 7 年。虽然它应该仍然可以在大多数浏览器中运行，但这里有一个基于@TypeError 建议的更新版本，它只能在更现代的浏览器中运行，iOS Safari 可能除外（可能支持也可能不支持responseType = 'blob'- 请务必测试！）：

var xhr = new XMLHttpRequest();
xhr.open('get', 'doodle.png', true);

// Load the data directly as a Blob.
xhr.responseType = 'blob';

xhr.onload = () => {
  document.querySelector('#myimage').src = URL.createObjectURL(this.response);
};

xhr.send(); 

回答by Janus Troelsen

You can fetch a Bloband use window.URL.createObjectURL. This prevents building giant strings and copying everything a couple of times.

您可以获取 aBlob并使用window.URL.createObjectURL. 这可以防止构建巨大的字符串并多次复制所有内容。

var xhr = new XMLHttpRequest();
xhr.open('GET', 'https://i.imgur.com/sBJOoTm.png', true);

xhr.responseType = 'blob';

xhr.onload = function(e) {
  if (this.status == 200) {
var blob = this.response;
document.getElementById("myImage").src = window.URL.createObjectURL(blob);
  }
};

xhr.onerror = function(e) {
  alert("Error " + e.target.status + " occurred while receiving the document.");
};

xhr.send();

<img id="myImage">

Example (same code): http://jsfiddle.net/ysangkok/sJxXk/86/. Works in Firefox and Chrome 25+. And all other browsers except Opera Mini: http://caniuse.com/#search=Blob

示例（相同代码）：http: //jsfiddle.net/ysangkok/sJxXk/86/。适用于 Firefox 和 Chrome 25+。以及除 Opera Mini 之外的所有其他浏览器：http: //caniuse.com/#search=Blob

回答by Yash

XMLHttpRequest

XMLHttpRequest

var xmlhttp = new XMLHttpRequest();
xmlhttp.open('GET', 'http://RestServiceURL-Returns Image', true);
xmlhttp.setRequestHeader('Content-type','application/x-www-form-urlencoded');
xmlhttp.responseType = 'arraybuffer/blob';
xmlhttp.send();

creating blob image in 3-ways.

以 3 种方式创建 blob 图像。

• window.URL.createObjectURL
• FileReader(caniuse)

• Base64String

  xmlhttp.onload = function() {
      var blob = new Blob([this.response], {type: 'image/png'}); 
      console.log(blob, blob.type, this.response, typeof this.response);  
  
      var image = document.getElementById('my-image');
  
      1)image.src = window.URL.createObjectURL(blob);
  
      2)var fileReader = new window.FileReader();
      fileReader.readAsDataURL(blob);
      fileReader.onloadend = function() { 
      image.src = fileReader.result;
      }
  
      3)var base64String = btoa(String.fromCharCode.apply(null, new Uint8Array(this.response)));
      image.src = 'data:image/png;base64,'+base64String;
  };
  

• 窗口.URL。创建对象URL
• FileReader( caniuse)

• Base64字符串

  xmlhttp.onload = function() {
      var blob = new Blob([this.response], {type: 'image/png'}); 
      console.log(blob, blob.type, this.response, typeof this.response);  
  
      var image = document.getElementById('my-image');
  
      1)image.src = window.URL.createObjectURL(blob);
  
      2)var fileReader = new window.FileReader();
      fileReader.readAsDataURL(blob);
      fileReader.onloadend = function() { 
      image.src = fileReader.result;
      }
  
      3)var base64String = btoa(String.fromCharCode.apply(null, new Uint8Array(this.response)));
      image.src = 'data:image/png;base64,'+base64String;
  };
  

Converting ArrayBuffer to Blobto ArrayBuffer

将 ArrayBuffer 转换为Blob到 ArrayBuffer

1)var dataView = new DataView(arrayBuffer);
var blob = new Blob([dataView], { type: mimeString });


2)fileReader.readAsArrayBuffer(blob);
var arrayBuffer;
fileReader.onload = function() {
    arrayBuffer = this.result;
};

回答by Jakob E

Same solution as suggested by Janus Troelsenwith promise added...

与Janus Troelsen建议的解决方案相同，并添加了承诺......

Note!when using createObjectURL- don't forget to call revokeObjectURL

笔记！使用createObjectURL 时- 不要忘记调用revokeObjectURL

//  Load blob (promise)
function loadBlob( url ){
    return new Promise( (resolve, reject) => {
        const xhr = new XMLHttpRequest();
        xhr.open('GET', url, true);
        xhr.responseType = 'blob';        
        xhr.onload  = () => resolve(xhr.response);
        xhr.onerror = () => reject(xhr.statusText);        
        xhr.send();
    });
}

//  Create image from blob (createObjectURL)
function imageFromBlob( blob ){ 
    const img = new Image();
    img.onload = () => URL.revokeObjectURL(img.src);
    img.src = URL.createObjectURL(blob);    
    return img;
}


//  Create image from blob if loaded successfully
loadBlob('https://unsplash.it/960/540?random')
    .then( blob => {
        document.body.appendChild( imageFromBlob(blob) );      
    })
    .catch( error => {
        console.log('Could not load image');
    })
    


//  Alternate version adding promise to xhr
//  if you like to trigger xhr.send() yourself
function xhrBlob(url){
    const xhr = new XMLHttpRequest();
    xhr.open('GET', url, true);
    xhr.responseType = 'blob';        
    xhr.promise = new Promise((resolve, reject) => {
        xhr.onload  = () => resolve(xhr.response);
        xhr.onerror = () => reject(xhr.statusText);  
    });
    xhr.load = ( onsuccess = () => {}, onerror = () => {} ) => { 
        xhr.promise.then(onsuccess).catch(onerror);
        xhr.send();
        return xhr;
    }
    return xhr;
}


//  Using load callbacks
xhrBlob('https://unsplash.it/960/540?random')
    .load( 
        //  on sussess
        blob => {
            document.body.appendChild( imageFromBlob(blob) );      
        },
        //  on error
        error => {
            console.log('Could not load image');
        }
    );
    
 //  Using promise (delayed)
const image = xhrBlob('https://unsplash.it/960/540?random');

    //  Promise handlers
    image.promise
    .then( blob => {
        document.body.appendChild( imageFromBlob(blob) );      
    })
    .catch( error => {
        console.log('Could not load image');
    });
 
 //  Load image (will trigger promise handlers)
 setTimeout(image.load, 3000);

img {
  width: 100%;
}