一番カンタンな方法 axiosの第3引数にoptionを渡す。コードはaxiosのgithubから抜粋 document.getElementById('upload').onclick = function () { var data = new FormData(); data.append('foo', 'bar'); data.append('file', document.getElementById('file').files[0]); var config = { onUploadProgress: function(progressEvent) { var percentCompleted = Math.round( (progressEvent.loaded * 100) / progressEvent.total ); } }; axios.put('/upload/s