How do I append a file to FormData()?

Question

fd.append("upload", file) yields,

------WebKitFormBoundaryJnjpATRkxe2Duwwu
Content-Disposition: form-data; name="userid"

8022171621665209152
------WebKitFormBoundaryJnjpATRkxe2Duwwu
Content-Disposition: form-data; name="upload"; filename="sample.csv"
Content-Type: text/csv


------WebKitFormBoundaryJnjpATRkxe2Duwwu--

fd.append("upload", evt.target.result) yields,

------WebKitFormBoundaryITfVxS7FbNWfk3Ty
Content-Disposition: form-data; name="userid"

8022171621665209152
------WebKitFormBoundaryITfVxS7FbNWfk3Ty
Content-Disposition: form-data; name="upload"

"Healthy1.jpg","1","3","1","5"
"Unhealthy1.jpg","0","2","1","2"
"Water1.jpg","2","2","1","3"
------WebKitFormBoundaryITfVxS7FbNWfk3Ty--

But I need this,

------WebKitFormBoundaryITfVxS7FbNWfk3Ty
Content-Disposition: form-data; name="userid"

8022171621665209152
------WebKitFormBoundaryITfVxS7FbNWfk3Ty
Content-Disposition: form-data; name="upload"; filename="sample.csv"
Content-Type: text/csv

"Healthy1.jpg","1","3","1","5"
"Unhealthy1.jpg","0","2","1","2"
"Water1.jpg","2","2","1","3"
------WebKitFormBoundaryITfVxS7FbNWfk3Ty--

Here is my code:

app.ports.uploadFile.subscribe(function(userid){
    var file = document.getElementById("csv").files[0];
    var fr = new FileReader();
    fr.readAsText(file, "UTF-8");
    fr.onload = function (evt) {
        console.log(evt.target.result);
        var fd = new FormData();
        fd.append("userid", userid)
        fd.append("upload", file) // <<<<< WHAT DO I PUT HERE?
        var xhr = new XMLHttpRequest()
        xhr.open('post', "http://localhost:8668/upload/ugimgset", true)
        xhr.setRequestHeader("Content-Type", "multipart/form-data")
        xhr.setRequestHeader("Authorization", "Bearer " + token() )
        xhr.send(fd)
    }
})

maybe http://stackoverflow.com/questions/21044798/how-to-use-formdata-for-ajax-file-upload helps — Jaromanda X, Apr 06 '17 at 04:28
thanks, but i don't want to use jQuery. But that is helpful - maybe i need to select the whole form, not just the input! i will try this — broinjc, Apr 06 '17 at 04:35
What is purpose of using `FileReader`? `javascript` at Question appears to return expected result — guest271314, Apr 06 '17 at 05:06
_"fd.append("upload", file) yields"_ Cannot reproduce multipart/form-data result described at Question using `javascript` at first example — guest271314, Apr 06 '17 at 05:18
@broinjc - the code in the accepted answer with the comment `// Attach file` is what I was trying to point you to — Jaromanda X, Apr 06 '17 at 05:23
@JaromandaX Note, the `javascript` at `fd.append("upload", file)` produces expected multipart/form-data described below _"But I need this"_ at OP — guest271314, Apr 06 '17 at 05:25
PEBCAK is the only point of failure I can't resolve :( Are you saying fd.append("upload", evt.target.result) is correct and perhaps it is a server side issue not processing the file correctly? — broinjc, Apr 06 '17 at 15:56
@broinjc `FileReader` is not necessary. `fd.append("upload", file)` yields expected result described at OP — guest271314, Apr 06 '17 at 16:56

score 3 · Accepted Answer · answered Apr 08 '17 at 00:16

I found the sources of my errors

I only needed FormData() - it takes care of the file and hidden fields.
I was overwriting Content-Type. Form boundaries were lost when I did this:

`xhr.setRequestHeader("Content-Type", "multipart/form-data")

The corrected code is below (along with some context):

app.ports.uploadFile.subscribe(function(pathAndId){
    var [tasksrvPath, formId] = pathAndId
    try {
        var fd = new FormData(document.getElementById(formId));
        var r = new XMLHttpRequest()
        r.open("POST", tasksrvPath, true)
        r.setRequestHeader("Authorization", "Bearer " + token() )
        r.send(fd)
        r.onload = function() {
            app.ports.status.send(r.statusText)
        }
    } catch(e) {
        console.log(e.message);
    }
})

How do I append a file to FormData()?

1 Answers1

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