upload_image_to_gyazo_using_fetch_api.js

var gyazo_data = {
    client_id: "ID_HERE",
    image_url: "IMAGE_URL",
    referer_url: "URL"
};
var form_data = new FormData();
for (var key in gyazo_data) {
    form_data.append(key, gyazo_data[key]);
}

fetch('https://upload.gyazo.com/api/upload/easy_auth', {
    method: 'POST',
    mode: 'cors',
    body: form_data
}).then(response => {
    return response.json();
}).then(function(json) {
    console.log(json)
});