ArrayBuffer to base64 encoded string

Question

I need an efficient  read native  way to convert an ArrayBuffer to a base64 string which needs to be used on a multipart post

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By my side  using Chrome navigator  I had to use DataView   to read an arrayBuffer  function  arrayBufferToBase64  tabU8A     var binary       let lecteur de donnees   new DataView tabU8A   var len   lecteur de donnees byteLength  var chaine       var pos1  for  var i   0  i  lt  len  i          binary    String fromCharCode  lecteur de donnees getUint8  i        chaine   window btoa  binary   return chaine

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var blob   new Blob  arrayBuffer    var reader   new FileReader    reader onload   function event      var base64     event target result     reader readAsDataURL blob

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The OP did not specify the Running Enviroment but if you are using Node JS there is a very simple way to do such thing   Accordig with the official Node JS docs  https   nodejs org api buffer html buffer buffers and character encodings     This step is only necessary if you don t already have a Buffer Object const buffer   Buffer from yourArrayBuffer    const base64String   buffer toString  base64      Also  If you are running under Angular for example  the Buffer Class will also be made available in a Browser Environment

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Below are 2 simple functions for converting Uint8Array to Base64 String and back again  arrayToBase64String a        return btoa String fromCharCode    a       base64StringToArray s        let asciiString   atob s       return new Uint8Array     asciiString  map char   gt  char charCodeAt 0

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You can derive a normal array from the ArrayBuffer by using Array prototype slice   Use a function like Array prototype map to convert bytes in to characters and join them together to forma  string   function arrayBufferToBase64 ab        var dView   new Uint8Array ab       Get a byte view              var arr   Array prototype slice call dView     Create a normal array              var arr1   arr map function item                 return String fromCharCode item        Convert              return window btoa arr1 join           Form a string      This method is faster since there are no string concatenations running in it

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This works fine for me   var base64String   btoa String fromCharCode apply null  new Uint8Array arrayBuffer       In ES6  the syntax is a little simpler   let base64String   btoa String fromCharCode    new Uint8Array arrayBuffer       As pointed out in the comments  this method may result in a runtime error in some browsers when the ArrayBuffer is large  The exact size limit is implementation dependent in any case

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function  arrayBufferToBase64 uarr        var strings       chunksize   0xffff      var len   uarr length       for  var i   0  i   chunksize  lt  len  i             strings push String fromCharCode apply null  uarr subarray i   chunksize   i   1    chunksize                return strings join          This is better  if you use JSZip for unpack archive from string

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For those who like it short  here s an other one using Array reduce which will not cause stack overflow   var base64   btoa    new Uint8Array arrayBuffer       reduce  data  byte    gt  data   String fromCharCode byte

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I used this and works for me   function arrayBufferToBase64  buffer         var binary           var bytes   new Uint8Array  buffer        var len   bytes byteLength      for  var i   0  i  lt  len  i              binary    String fromCharCode  bytes  i                return window btoa  binary         function base64ToArrayBuffer base64        var binary string    window atob base64       var len   binary string length      var bytes   new Uint8Array  len        for  var i   0  i  lt  len  i                     bytes i    binary string charCodeAt i             return bytes buffer

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There is another asynchronous way use Blob and FileReader   I didn t test the performance  But it is a different way of thinking   function arrayBufferToBase64  buffer  callback         var blob   new Blob  buffer   type  application octet-binary         var reader   new FileReader        reader onload   function evt           var dataurl   evt target result          callback dataurl substr dataurl indexOf      1               reader readAsDataURL blob        example  var buf   new Uint8Array  11 22 33    arrayBufferToBase64 buf  console log bind console       CxYh

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function  arrayBufferToBase64  buffer         var binary           var bytes   new Uint8Array  buffer        var len   bytes byteLength      for  var i   0  i  lt  len  i              binary    String fromCharCode  bytes  i                return window btoa  binary        but  non-native implementations are faster e g  https   gist github com 958841 see http   jsperf com encoding-xhr-image-data 6

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My recommendation for this is to NOT use native btoa strategies   as they don t correctly encode all ArrayBuffer s     rewrite the DOMs atob   and btoa       Since DOMStrings are 16-bit-encoded strings  in most browsers calling window btoa on a Unicode string will cause a Character Out Of Range exception if a character exceeds the range of a 8-bit ASCII-encoded character    While I have never encountered this exact error  I have found that many of the ArrayBuffer s I have tried to encode have encoded incorrectly   I would either use MDN recommendation or gist    https   github com beatgammit base64-js https   gist github com jonleighton 958841

[javascript] ArrayBuffer to base64 encoded string

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