diff --git a/frontends/ycdl_flask/static/js/api.js b/frontends/ycdl_flask/static/js/api.js
index 774c9af..c887dee 100644
--- a/frontends/ycdl_flask/static/js/api.js
+++ b/frontends/ycdl_flask/static/js/api.js
@@ -7,8 +7,7 @@ api.channels.add_channel =
 function add_channel(channel_id, callback)
 {
     const url = "/add_channel";
-    const data = new FormData();
-    data.append("channel_id", channel_id);
+    const data = {"channel_id": channel_id};
     return common.post(url, data, callback);
 }
 
@@ -16,7 +15,7 @@ api.channels.delete_channel =
 function delete_channel(channel_id, callback)
 {
     const url = `/channel/${channel_id}/delete`;
-    const data = new FormData();
+    const data = {};
     return common.post(url, data, callback);
 }
 
@@ -24,8 +23,7 @@ api.channels.refresh_channel =
 function refresh_channel(channel_id, force, callback)
 {
     const url = `/channel/${channel_id}/refresh`;
-    const data = new FormData();
-    data.append("force", force)
+    const data = {"force": force};
     return common.post(url, data, callback);
 }
 
@@ -33,8 +31,7 @@ api.channels.refresh_all_channels =
 function refresh_all_channels(force, callback)
 {
     const url = "/refresh_all_channels";
-    const data = new FormData();
-    data.append("force", force)
+    const data = {"force": force};
     return common.post(url, data, callback);
 }
 
@@ -42,8 +39,7 @@ api.channels.set_automark =
 function set_automark(channel_id, state, callback)
 {
     const url = `/channel/${channel_id}/set_automark`;
-    const data = new FormData();
-    data.append("state", state);
+    const data = {"state": state};
     return common.post(url, data, callback);
 }
 
@@ -51,8 +47,7 @@ api.channels.set_download_directory =
 function set_download_directory(channel_id, download_directory, callback)
 {
     const url = `/channel/${channel_id}/set_download_directory`;
-    const data = new FormData();
-    data.append("download_directory", download_directory);
+    const data = {"download_directory": download_directory};
     return common.post(url, data, callback);
 }
 
@@ -60,8 +55,7 @@ api.channels.set_queuefile_extension =
 function set_queuefile_extension(channel_id, extension, callback)
 {
     const url = `/channel/${channel_id}/set_queuefile_extension`;
-    const data = new FormData();
-    data.append("extension", extension);
+    const data = {"extension": extension};
     return common.post(url, data, callback);
 }
 
@@ -85,9 +79,7 @@ api.videos.mark_state =
 function mark_state(video_ids, state, callback)
 {
     const url = "/mark_video_state";
-    const data = new FormData();
-    data.append("video_ids", video_ids);
-    data.append("state", state);
+    const data = {"video_ids": video_ids, "state": state};
     return common.post(url, data, callback);
 }
 
@@ -95,7 +87,6 @@ api.videos.start_download =
 function start_download(video_ids, callback)
 {
     const url = "/start_download";
-    const data = new FormData();
-    data.append("video_ids", video_ids);
+    const data = {"video_ids": video_ids};
     return common.post(url, data, callback);
 }
diff --git a/frontends/ycdl_flask/static/js/common.js b/frontends/ycdl_flask/static/js/common.js
index 232be97..5be4e09 100644
--- a/frontends/ycdl_flask/static/js/common.js
+++ b/frontends/ycdl_flask/static/js/common.js
@@ -55,6 +55,25 @@ function refresh_or_alert(response)
 // HTTP ////////////////////////////////////////////////////////////////////////////////////////////
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
+common.formdata =
+function formdata(data)
+{
+    fd = new FormData();
+    for (let [key, value] of Object.entries(data))
+    {
+        if (value === undefined)
+        {
+            continue;
+        }
+        if (value === null)
+        {
+            value = '';
+        }
+        fd.append(key, value);
+    }
+    return fd;
+}
+
 common._request =
 function _request(method, url, callback)
 {
@@ -143,8 +162,18 @@ common.post =
 function post(url, data, callback)
 {
     /*
-    `data`: a FormData object which you have already filled with values.
+    `data`:
+        a FormData object which you have already filled with values, or a
+        dictionary from which a FormData will be made, using common.formdata.
     */
+    if (data instanceof FormData || data === null)
+    {
+        ;
+    }
+    else
+    {
+        data = common.formdata(data);
+    }
     request = common._request("POST", url, callback);
     request.send(data);
     return request;