From 3c3b8397bc0e881b2378cb58e83b388604b2b4a3 Mon Sep 17 00:00:00 2001
From: archmoj <mojtaba@plot.ly>
Date: Fri, 9 Oct 2020 11:04:49 -0400
Subject: [PATCH 1/4] provide the list of all valid export formats in toImage
 warning

---
 src/lib/index.js                   | 17 +++++++++++++++++
 src/plot_api/to_image.js           |  2 +-
 test/jasmine/tests/toimage_test.js |  2 +-
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/lib/index.js b/src/lib/index.js
index 157dd15542b..3189f785b8b 100644
--- a/src/lib/index.js
+++ b/src/lib/index.js
@@ -1244,3 +1244,20 @@ lib.ensureUniformFontSize = function(gd, baseFont) {
     );
     return out;
 };
+
+/**
+ * provide a human-readable lists with an optional ending separator such as A, B, C and D
+ *
+ * @param {array} arr : the array to join
+ * @param {string} mainSeparator : main separator
+ * @param {string} lastSeparator : optional last separator
+ *
+ * @return {string} : joined list
+ */
+lib.join2 = function(arr, mainSeparator, lastSeparator) {
+    var len = arr.length;
+    if(len > 2 && lastSeparator) {
+        return arr.slice(0, -1).join(mainSeparator) + lastSeparator + arr[len - 1];
+    }
+    return arr.join(mainSeparator);
+};
diff --git a/src/plot_api/to_image.js b/src/plot_api/to_image.js
index 11491416f01..e0e3f4c18bd 100644
--- a/src/plot_api/to_image.js
+++ b/src/plot_api/to_image.js
@@ -116,7 +116,7 @@ function toImage(gd, opts) {
     }
 
     if(!isImpliedOrValid('format')) {
-        throw new Error('Image format is not jpeg, png, svg or webp.');
+        throw new Error('Export format is not ' + Lib.join2(attrs.format.values, ', ', ' or ') + '.');
     }
 
     var fullOpts = {};
diff --git a/test/jasmine/tests/toimage_test.js b/test/jasmine/tests/toimage_test.js
index 5baac3d2445..fdbe1ce6bdf 100644
--- a/test/jasmine/tests/toimage_test.js
+++ b/test/jasmine/tests/toimage_test.js
@@ -65,7 +65,7 @@ describe('Plotly.toImage', function() {
         Plotly.plot(gd, fig.data, fig.layout)
         .then(function(gd) {
             expect(function() { Plotly.toImage(gd, {format: 'x'}); })
-                .toThrow(new Error('Image format is not jpeg, png, svg or webp.'));
+                .toThrow(new Error('Export format is not png, jpeg, webp, svg or full-json.'));
         })
         .catch(failTest)
         .then(done);

From 5d91aa404c39521d50f55a7bf02e6c9703821ad7 Mon Sep 17 00:00:00 2001
From: Mojtaba Samimi <33888540+archmoj@users.noreply.github.com>
Date: Wed, 14 Oct 2020 10:53:44 -0400
Subject: [PATCH 2/4] correct length check

Co-authored-by: Alex Johnson <johnson.alex.c@gmail.com>
---
 src/lib/index.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/lib/index.js b/src/lib/index.js
index 3189f785b8b..c06d46a5381 100644
--- a/src/lib/index.js
+++ b/src/lib/index.js
@@ -1256,7 +1256,7 @@ lib.ensureUniformFontSize = function(gd, baseFont) {
  */
 lib.join2 = function(arr, mainSeparator, lastSeparator) {
     var len = arr.length;
-    if(len > 2 && lastSeparator) {
+    if(len > 1 && lastSeparator) {
         return arr.slice(0, -1).join(mainSeparator) + lastSeparator + arr[len - 1];
     }
     return arr.join(mainSeparator);

From c5dc44439e00d87942aa45c5723cb3949142437e Mon Sep 17 00:00:00 2001
From: archmoj <mojtaba@plot.ly>
Date: Wed, 14 Oct 2020 11:00:06 -0400
Subject: [PATCH 3/4] revise help for last separator

---
 src/lib/index.js | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/lib/index.js b/src/lib/index.js
index c06d46a5381..205b264de3a 100644
--- a/src/lib/index.js
+++ b/src/lib/index.js
@@ -1246,11 +1246,10 @@ lib.ensureUniformFontSize = function(gd, baseFont) {
 };
 
 /**
- * provide a human-readable lists with an optional ending separator such as A, B, C and D
+ * provide a human-readable list e.g. "A, B, C and D" with an ending separator
  *
  * @param {array} arr : the array to join
  * @param {string} mainSeparator : main separator
- * @param {string} lastSeparator : optional last separator
  *
  * @return {string} : joined list
  */

From 9ce11aaa9d14149f2f835910fdf8190748424aa2 Mon Sep 17 00:00:00 2001
From: archmoj <mojtaba@plot.ly>
Date: Wed, 14 Oct 2020 11:07:06 -0400
Subject: [PATCH 4/4] fixup last separator condition

---
 src/lib/index.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/lib/index.js b/src/lib/index.js
index 205b264de3a..17342b1a649 100644
--- a/src/lib/index.js
+++ b/src/lib/index.js
@@ -1250,12 +1250,13 @@ lib.ensureUniformFontSize = function(gd, baseFont) {
  *
  * @param {array} arr : the array to join
  * @param {string} mainSeparator : main separator
+ * @param {string} lastSeparator : last separator
  *
  * @return {string} : joined list
  */
 lib.join2 = function(arr, mainSeparator, lastSeparator) {
     var len = arr.length;
-    if(len > 1 && lastSeparator) {
+    if(len > 1) {
         return arr.slice(0, -1).join(mainSeparator) + lastSeparator + arr[len - 1];
     }
     return arr.join(mainSeparator);