Keep javascript blob from editing data when saving file

Question

I want to move data generated in javascript to a file

I am using

    function saveTextAsFile(textToWrite,FileName){
    var textFileAsBlob = new Blob([textToWrite], {type:'text/plain'});
    var downloadLink = document.createElement("a");
    downloadLink.download = FileName;
    downloadLink.innerHTML = "Download File";
    if (window.webkitURL != null){
        // Chrome allows the link to be clicked
        // without actually adding it to the DOM.
        downloadLink.href = window.webkitURL.createObjectURL(textFileAsBlob);
    }
    else{
        // Firefox requires the link to be added to the DOM
        // before it can be clicked.        
        downloadLink.href = window.URL.createObjectURL(textFileAsBlob);
        downloadLink.style.display = "none";
        document.body.appendChild(downloadLink);        
    }
    downloadLink.click();
    }

based on code from Is it possible to write data to file using only JavaScript?

The problem is that a 0xc2 is inserted before every character with ascii value above 0x79.

000041e0  30 35 5d 22 57 69 72 65  6c 65 73 73 22 3d 30 0a  |05]"Wireless"=0.|
000041f0  00 00 c2 b0 c2 a0 c2 80  7f                       |.........|
000041f9

This happened in both firefox & chromium browsers in Ubuntu Linux. I'm hoping that some other blob type besides 'text/plain' will not have this behavior, but I'm having trouble finding the relevant documentation.

Dustin Soodak

Note: this is a new approach to question Can you make a textarea which doesn't automatically edit your text? which seems to be impossible

above 0x79 - you mean 0x7f - because I see an 0x7f without a preceding 0xc2 — Jaromanda X
– Jaromanda X, Commented Nov 8, 2016 at 1:02
try type: 'text/plain; charset=iso-8859-1' - because that 0xc2 prefix is how UTF-8 chars from 0x80 to 0xBF are "encoded" - 0xC0 to 0xFF would get a 0xc3 prefix — Jaromanda X
– Jaromanda X, Commented Nov 8, 2016 at 1:08
yes, I meant 0x7f. I tried both of those but it still happened. also, c0->c380, c1->c381, etc. — Dustin Soodak
– Dustin Soodak, Commented Nov 8, 2016 at 16:47
Maybe it has something to do with initializing the blob with a string (even though I did a hex print on the last part of the string to make sure it was as expected) — Dustin Soodak
– Dustin Soodak, Commented Nov 8, 2016 at 16:49

Community · Accepted Answer · 2017-05-23 12:13:33Z

I added 'application/octet-binary' to my google search and found an answer at "Create binary blob in JS". It looks like if you initialize the blob from a Uint8Array instead of a string, it no longer alters the data. Here is the full working code:

    function saveTextAsFile(textToWrite,FileName){
       function destroyClickedElement(event){
            document.body.removeChild(event.target);
        }
        var byteArray = new Uint8Array(textToWrite.length);
        for (var i=0;i<byteArray.length;i++){
            byteArray[i]=textToWrite.charCodeAt(i);
        }
        var textFileAsBlob = new Blob([byteArray], {type:'application/octet-binary'});
        var downloadLink = document.createElement("a");
        downloadLink.download = FileName;
        downloadLink.innerHTML = "Download File";
        if (window.webkitURL != null){
            // Chrome allows the link to be clicked
            // without actually adding it to the DOM.
            downloadLink.href = window.webkitURL.createObjectURL(textFileAsBlob);
        }
        else{
            // Firefox requires the link to be added to the DOM
            // before it can be clicked.        
            downloadLink.href = window.URL.createObjectURL(textFileAsBlob);
            downloadLink.onclick = destroyClickedElement;   
            downloadLink.style.display = "none";
            document.body.appendChild(downloadLink);        
        }
        downloadLink.click();
    }

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