Consider substituting optional BlobPart or sequence<BlobPart> for optional sequence<BlobPart> blobParts at constructor #150

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1. guest271314 commented on Apr 5, 2020

   

   guest271314

   on Apr 5, 2020

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   Use case

   If new Blob(undefined) #33 can be handled to output

   Blob {size: 0, type: ""}

   Similarly

   new Blob(new Float32Array([0.00005549501292989589, 0.00006459458381868899, 0.000058644378441385925, 0.00006201512587722391]))

   should be handled to output

   file.arrayBuffer().then(b =>  console.log(new Float32Array(b))).catch(console.error);
   Promise {<pending>}
   Float32Array(4) [0.00005549501292989589, 0.00006459458381868899, 0.000058644378441385925, 0.00006201512587722391]
   

   rather than RangeError (Chromium RangeError: byte length of Float32Array should be a multiple of 4; Nightly RangeError: "attempting to construct out-of-bounds TypedArray on ArrayBuffer") due to

   file.text().then(console.log).catch(console.error); // new Blob(TypedArray)
   Promise {<pending>}
   0.000055495012929895890.000064594583818688990.0000586443784413859250.00006201512587722391
   

   instead of

   file.text().then(console.log).catch(console.error); // new Blob([TypedArray])
   Promise {<pending>}
   Q�h8�v�8��u8���8
   

   Will the suggested change break any existing API or be incompatible with implementation that uses File API expecting new Blob(TypedArray) to output a concatenated string of the members of the passed TypedArray?
2. domenic commented on Apr 5, 2020

   

   domenic

   on Apr 5, 2020

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   It seems the use case here is allowing you to avoid typing [ and ]. I'm not sure that's worth the churn.

   👍React with 👍2Reacted by Anne van Kesteren and Kagami Sascha Rosylight
3. guest271314 commented on Apr 5, 2020

   

   guest271314

   on Apr 5, 2020

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   Actually the use of [] is not particularly problematic from a front-end coding perspective. It is not clearly specified that, or Set is required to avoid conversion to string, at least not immediately clear in plain language at the specification, that could disambiguate from no use of []. Consistency is the purpose of the suggestion: Why does new Blob(void 0) // new Blob(undefined) not output Blob {size: 6, type: ""} or Blob {size: 9, type: ""} if in fact any value not within [] or Set is converted to string?

   The change will avoid unexpected results when [] is not used.

   If the change is not worth it from a specification perspective a note describing that to avoid string conversion for the case of new Blob(TypedArray), new Blob([TypedArray]) should be used. That is, if including a note clarifying the case is not expensive: it would certainly be useful for readers of specification, and a reference point.
4. guest271314 commented on Apr 5, 2020

   

   guest271314

   on Apr 5, 2020

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   The adjacent, or opposite, case is passing an array of TypedArrays, to Blob() with [] included, e.g., new Blob([[Uint8Array, Uint8Array, ..., Uint8Array]]) where when the data is attempted to be converted back to original values, the result will not be expected. In brief,

             Promise.all(promises)
             .then(result => {
               console.log(result); // (890) [Uint8Array(36), Uint8Array(38), ... Uint8Array(38)]
               /*
                 0: Uint8Array(36) [82, 73, 70, 70, 28, 0, 0, 0, 87, 69, 66, 80, 86, 80, 56, 76, 16, 0, 0, 0, 47, 149, 64, 37, 0, 7, 80, 194, 168, 66, 255, 3, 17, 209, 255, 0]
                 ...
               */
               let blob, file;
               // RangeError: Invalid string length
               // Array.join (<anonymous>)
               // Array.toString (<anonymous>)
               try {
                 blob = new Blob([result]);
                 console.log(blob);
                 blob.arrayBuffer().then(buffer => {
                   console.log(new Uint8Array(buffer)); // Uint8Array(94848) [56, 50, 44, 55, 51, 44, 55, 48, 44, 55, 48, 44, 50, 56, 44, 48, 44, 48, 44, 48, 44, 56, 55
                 })
               } catch (e) {
                   console.error(e);
               }
             });
   

   Now, if we try we will get an error

   createImageBitmap(new Blob([new Uint8Array([56, 50, 44, 55, 51, 44, 55, 48, 44, 55, 48, 44, 50, 56, 44, 48, 44, 48, 44, 48, 44, 56, 55, 44, 54, 57, 44, 54, 54, 44, 56, 48, 44, 56, 54, 44])]))
   .then(console.log).catch(console.error);
   Promise {<pending>}
   663a7444cff629a41b76.js:109 DOMException: The source image could not be decoded.
   

   where if we got back the same results we will get

   createImageBitmap(new Blob([new Uint8Array([82, 73, 70, 70, 28, 0, 0, 0, 87, 69, 66, 80, 86, 80, 56, 76, 16, 0, 0, 0, 47, 149, 64, 37, 0, 7, 80, 194, 168, 66, 255, 3, 17, 209, 255, 0])]))
   .then(console.log);
   Promise {<pending>}
   663a7444cff629a41b76.js:109 ImageBitmap {width: 150, height: 150}
   

   What happened to the original input data? Simply using [] directly affected the result when converting back to original data?

   Evidently, yes. In this case, potentially relatively common, the resulting promise value from Promise.all(), we do not need to use []

             Promise.all(promises)
             .then(result => {
               console.log(result); // (892) [Uint8Array(36), Uint8Array(36), Uint8Array(38)...]
               /*
               0: Uint8Array(36) [82, 73, 70, 70, 28, 0, 0, 0, 87, 69, 66, 80, 86, 80, 56, 76, 16, 0, 0, ...]
               */
               let blob, file;
               // RangeError: Invalid string length
               // Array.join (<anonymous>)
               // Array.toString (<anonymous>)
               try {
                 blob = new Blob(result);
                 console.log(blob); // Blob {size: 33164, type: ""}
                 blob.arrayBuffer().then(buffer => {
                   // now we can use subarray(), slice(), ReadableStream/WritableStream, etc. to re-create the ImageBitmap, in sequence, or by specific offset(s)
                   console.log(new Uint8Array(buffer)); // Uint8Array(33164) [82, 73, 70, 70, 28, 0, 0, 0, 87, 69, 66, 80, 86, 80, 56, 76, 16, 0, 0, 0, ...]
                 })
               } catch (e) {
                   console.error(e);
               }
               ...
            })
   
5. guest271314 commented on Apr 5, 2020

   

   guest271314

   on Apr 5, 2020

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   Or, are the above examples simply relegated to PEBCAK, without need for note to user re use of [] or not at Blob constructor? If so, kindly close the issue.
6. guest271314 commented on May 14, 2020

   

   guest271314

   on May 14, 2020

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   From the wild https://stackoverflow.com/questions/61620389/how-to-load-previous-state-of-file-field-in-react#comment109152574_61620572 at https://stackoverflow.com/q/61620389

   However, somehow I cannot completely solve the problem by using your code. It is not possible to create a file from the incoming form data. TypeError: Failed to construct 'File': The provided value cannot be converted to a sequence. – dan_boy May 10 at 7:40

   Am not sure what response.data.file is or expected to be in the code.