How to upload string as file with jQuery or other js framework

Here's how to do it without manually building the multi-part request body:

var s = 'some string data';var filename = 'foobar.txt';var formData = new FormData();formData.append('file', new File([new Blob([s])], filename));formData.append('another-form-field', 'some value');$.ajax({    url: '/upload',    data: formData,    processData: false,    contentType: false,    type: 'POST',    success: function () {        console.log('ok');    },    error: function () {        console.log('err'); // replace with proper error handling    }});

You need to set the Content-type request header to multipart/form-data and play around with the format a little, I wrote this in Plain Ol' JavaScript (tm) but you could easily rework it for a library:

EDIT: had my coffee now, so modified it for jQuery (no-library version here):

// Define a boundary, I stole this from IE but you can use any string AFAIKvar boundary = "---------------------------7da24f2e50046";var body = '--' + boundary + '\r\n'         // Parameter name is "file" and local filename is "temp.txt"         + 'Content-Disposition: form-data; name="file";'         + 'filename="temp.txt"\r\n'         // Add the file's mime-type         + 'Content-type: plain/text\r\n\r\n'         // Add your data:         + data + '\r\n'         + '--'+ boundary + '--';$.ajax({    contentType: "multipart/form-data; boundary="+boundary,    data: body,    type: "POST",    url: "http://asite.com/apage.php",    success: function (data, status) {    }});

Solution using new FormData() without ajax

str = "Hello!\nI'm text string";var strblob = new Blob([str], {type: 'text/plain'});var formdata = new FormData();formdata.append("file", strblob, "file.txt");formdata.append("field-1", "field-1-data");var requestOptions = {  method: 'POST',  body: formdata,  redirect: 'follow'};fetch("http://{url}", requestOptions)  .then(response => response.text())  .then(result => console.log(result))  .catch(error => console.log('error', error))