ฉันต้องการแปลงสตริงเข้ารหัส base64 เป็น ArrayBuffer สตริง base64 คืออินพุตของผู้ใช้ซึ่งจะถูกคัดลอกและวางจากอีเมลดังนั้นจึงไม่อยู่ที่นั่นเมื่อโหลดเพจ ฉันต้องการทำสิ่งนี้ใน javascript โดยไม่ต้องเรียก ajax ไปที่เซิร์ฟเวอร์ถ้าเป็นไปได้

ฉันพบว่าลิงก์เหล่านั้นน่าสนใจ แต่พวกเขาไม่ได้ช่วยฉัน:

ArrayBuffer เป็นสตริงที่เข้ารหัส base64

นี่คือเกี่ยวกับการแปลงตรงกันข้ามจาก ArrayBuffer เป็น base64 ไม่ใช่ในทางกลับกัน

http://jsperf.com/json-vs-base64/2

มันดูดี แต่ฉันหาวิธีใช้รหัสไม่ได้

มีวิธีง่ายๆในการแปลงหรือไม่? ขอบคุณ

ลองสิ่งนี้:

function _base64ToArrayBuffer(base64) {
    var binary_string = window.atob(base64);
    var len = binary_string.length;
    var bytes = new Uint8Array(len);
    for (var i = 0; i < len; i++) {
        bytes[i] = binary_string.charCodeAt(i);
    }
    return bytes.buffer;
}

Using TypedArray.from:

Uint8Array.from(atob(base64_string), c => c.charCodeAt(0))

Performance to be compared with the for loop version of Goran.it answer.

Goran.it's answer does not work because of unicode problem in javascript - https://developer.mozilla.org/en-US/docs/Web/API/WindowBase64/Base64_encoding_and_decoding.

I ended up using the function given on Daniel Guerrero's blog: http://blog.danguer.com/2011/10/24/base64-binary-decoding-in-javascript/

Function is listed on github link: https://github.com/danguer/blog-examples/blob/master/js/base64-binary.js

Use these lines

var uintArray = Base64Binary.decode(base64_string);  
var byteArray = Base64Binary.decodeArrayBuffer(base64_string); 

Just found base64-arraybuffer, a small npm package with incredibly high usage, 5M downloads last month (2017-08).

https://www.npmjs.com/package/base64-arraybuffer

For anyone looking for something of a best standard solution, this may be it.

Async solution, it's better when the data is big:

// base64 to buffer
function base64ToBufferAsync(base64) {
  var dataUrl = "data:application/octet-binary;base64," + base64;

  fetch(dataUrl)
    .then(res => res.arrayBuffer())
    .then(buffer => {
      console.log("base64 to buffer: " + new Uint8Array(buffer));
    })
}

// buffer to base64
function bufferToBase64Async( buffer ) {
    var blob = new Blob([buffer], {type:'application/octet-binary'});    
    console.log("buffer to blob:" + blob)

    var fileReader = new FileReader();
    fileReader.onload = function() {
      var dataUrl = fileReader.result;
      console.log("blob to dataUrl: " + dataUrl);

      var base64 = dataUrl.substr(dataUrl.indexOf(',')+1)      
      console.log("dataUrl to base64: " + base64);
    };
    fileReader.readAsDataURL(blob);
}

For Node.js users:

const myBuffer = Buffer.from(someBase64String, 'base64');

myBuffer will be of type Buffer which is a subclass of Uint8Array. Unfortunately, Uint8Array is NOT an ArrayBuffer as the OP was asking for. But when manipulating an ArrayBuffer I almost always wrap it with Uint8Array or something similar, so it should be close to what's being asked for.

Javascript is a fine development environment so it seems odd than it doesn't provide a solution to this small problem. The solutions offered elsewhere on this page are potentially slow. Here is my solution. It employs the inbuilt functionality that decodes base64 image and sound data urls.

var req = new XMLHttpRequest;
req.open('GET', "data:application/octet;base64," + base64Data);
req.responseType = 'arraybuffer';
req.onload = function fileLoaded(e)
{
   var byteArray = new Uint8Array(e.target.response);
   // var shortArray = new Int16Array(e.target.response);
   // var unsignedShortArray = new Int16Array(e.target.response);
   // etc.
}
req.send();

The send request fails if the base 64 string is badly formed.

The mime type (application/octet) is probably unnecessary.

Tested in chrome. Should work in other browsers.

Pure JS - no string middlestep (no atob)

I write following function which convert base64 in direct way (without conversion to string at the middlestep). IDEA

• get 4 base64 characters chunk
• find index of each character in base64 alphabet
• convert index to 6-bit number (binary string)
• join four 6 bit numbers which gives 24-bit numer (stored as binary string)
• split 24-bit string to three 8-bit and covert each to number and store them in output array
• corner case: if input base64 string ends with one/two = char, remove one/two numbers from output array

Below solution allows to process large input base64 strings. Similar function for convert bytes to base64 without btoa is HERE

function base64ToBytesArr(str) {
  const abc = [..."ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"]; // base64 alphabet
  let result = [];

  for(let i=0; i<str.length/4; i++) {
    let chunk = [...str.slice(4*i,4*i+4)]
    let bin = chunk.map(x=> abc.indexOf(x).toString(2).padStart(6,0)).join(''); 
    let bytes = bin.match(/.{1,8}/g).map(x=> +('0b'+x));
    result.push(...bytes.slice(0,3 - (str[4*i+2]=="=") - (str[4*i+3]=="=")));
  }
  return result;
}


// --------
// TEST
// --------


let test = "Alice's Adventure in Wonderland.";  

console.log('test string:', test.length, test);
let b64_btoa = btoa(test);
console.log('encoded string:', b64_btoa);

let decodedBytes = base64ToBytesArr(b64_btoa); // decode base64 to array of bytes
console.log('decoded bytes:', JSON.stringify(decodedBytes));
let decodedTest = decodedBytes.map(b => String.fromCharCode(b) ).join``;
console.log('Uint8Array', JSON.stringify(new Uint8Array(decodedBytes)));
console.log('decoded string:', decodedTest.length, decodedTest);

I would strongly suggest using an npm package implementing correctly the base64 specification.

The best one I know is rfc4648

The problem is that btoa and atob use binary strings instead of Uint8Array and trying to convert to and from it is cumbersome. Also there is a lot of bad packages in npm for that. I lose a lot of time before finding that one.

The creators of that specific package did a simple thing: they took the specification of Base64 (which is here by the way) and implemented it correctly from the beginning to the end. (Including other formats in the specification that are also useful like Base64-url, Base32, etc ...) That doesn't seem a lot but apparently that was too much to ask to the bunch of other libraries.

So yeah, I know I'm doing a bit of proselytism but if you want to avoid losing your time too just use rfc4648.

const str = "dGhpcyBpcyBiYXNlNjQgc3RyaW5n"
const encoded = new TextEncoder().encode(str) // is Uint8Array
const buf = encoded.buffer // is ArrayBuffer