[Fix] stringify: with arrayFormat: comma, properly include an explicit [] on a single-item array

Properly fixes #434

Author: ljharb

.eslintrc

@@ -15,7 +15,7 @@
         "indent": [2, 4],
         "max-lines-per-function": [2, { "max": 150 }],
         "max-params": [2, 15],
-        "max-statements": [2, 52],
+        "max-statements": [2, 53],
         "multiline-comment-style": 0,
         "no-continue": 1,
         "no-magic-numbers": 0,

lib/stringify.js

@@ -126,7 +126,7 @@ var stringify = function stringify(
                 for (var i = 0; i < valuesArray.length; ++i) {
                     valuesJoined += (i === 0 ? '' : ',') + formatter(encoder(valuesArray[i], defaults.encoder, charset, 'value', format));
                 }
-                return [formatter(keyValue) + (i === 1 ? '[]' : '') + '=' + valuesJoined];
+                return [formatter(keyValue) + (isArray(obj) && valuesArray.length === 1 ? '[]' : '') + '=' + valuesJoined];
             }
             return [formatter(keyValue) + '=' + formatter(encoder(obj, defaults.encoder, charset, 'value', format))];
         }
@@ -150,6 +150,8 @@ var stringify = function stringify(
         objKeys = sort ? keys.sort(sort) : keys;
     }
 
+    var adjustedPrefix = generateArrayPrefix === 'comma' && isArray(obj) && obj.length === 1 ? prefix + '[]' : prefix;
+
     for (var j = 0; j < objKeys.length; ++j) {
         var key = objKeys[j];
         var value = typeof key === 'object' && typeof key.value !== 'undefined' ? key.value : obj[key];
@@ -159,8 +161,8 @@ var stringify = function stringify(
         }
 
         var keyPrefix = isArray(obj)
-            ? typeof generateArrayPrefix === 'function' ? generateArrayPrefix(prefix, key) : prefix
-            : prefix + (allowDots ? '.' + key : '[' + key + ']');
+            ? typeof generateArrayPrefix === 'function' ? generateArrayPrefix(adjustedPrefix, key) : adjustedPrefix
+            : adjustedPrefix + (allowDots ? '.' + key : '[' + key + ']');
 
         sideChannel.set(object, step);
         var valueSideChannel = getSideChannel();

test/stringify.js

@@ -132,15 +132,32 @@ test('stringify()', function (t) {
     });
 
     t.test('stringifies an array value with one item vs multiple items', function (st) {
-        st.equal(qs.stringify({ a: ['c'] }, { encodeValuesOnly: true, arrayFormat: 'indices' }), 'a[0]=c');
-        st.equal(qs.stringify({ a: ['c'] }, { encodeValuesOnly: true, arrayFormat: 'brackets' }), 'a[]=c');
-        st.equal(qs.stringify({ a: ['c'] }, { encodeValuesOnly: true, arrayFormat: 'comma' }), 'a[]=c'); // so it parses back as an array
-        st.equal(qs.stringify({ a: ['c'] }, { encodeValuesOnly: true }), 'a[0]=c');
+        st.test('non-array item', function (s2t) {
+            s2t.equal(qs.stringify({ a: 'c' }, { encodeValuesOnly: true, arrayFormat: 'indices' }), 'a=c');
+            s2t.equal(qs.stringify({ a: 'c' }, { encodeValuesOnly: true, arrayFormat: 'brackets' }), 'a=c');
+            s2t.equal(qs.stringify({ a: 'c' }, { encodeValuesOnly: true, arrayFormat: 'comma' }), 'a=c');
+            s2t.equal(qs.stringify({ a: 'c' }, { encodeValuesOnly: true }), 'a=c');
 
-        st.equal(qs.stringify({ a: ['c', 'd'] }, { encodeValuesOnly: true, arrayFormat: 'indices' }), 'a[0]=c&a[1]=d');
-        st.equal(qs.stringify({ a: ['c', 'd'] }, { encodeValuesOnly: true, arrayFormat: 'brackets' }), 'a[]=c&a[]=d');
-        st.equal(qs.stringify({ a: ['c', 'd'] }, { encodeValuesOnly: true, arrayFormat: 'comma' }), 'a=c,d');
-        st.equal(qs.stringify({ a: ['c', 'd'] }, { encodeValuesOnly: true }), 'a[0]=c&a[1]=d');
+            s2t.end();
+        });
+
+        st.test('array with a single item', function (s2t) {
+            s2t.equal(qs.stringify({ a: ['c'] }, { encodeValuesOnly: true, arrayFormat: 'indices' }), 'a[0]=c');
+            s2t.equal(qs.stringify({ a: ['c'] }, { encodeValuesOnly: true, arrayFormat: 'brackets' }), 'a[]=c');
+            s2t.equal(qs.stringify({ a: ['c'] }, { encodeValuesOnly: true, arrayFormat: 'comma' }), 'a[]=c'); // so it parses back as an array
+            s2t.equal(qs.stringify({ a: ['c'] }, { encodeValuesOnly: true }), 'a[0]=c');
+
+            s2t.end();
+        });
+
+        st.test('array with multiple items', function (s2t) {
+            s2t.equal(qs.stringify({ a: ['c', 'd'] }, { encodeValuesOnly: true, arrayFormat: 'indices' }), 'a[0]=c&a[1]=d');
+            s2t.equal(qs.stringify({ a: ['c', 'd'] }, { encodeValuesOnly: true, arrayFormat: 'brackets' }), 'a[]=c&a[]=d');
+            s2t.equal(qs.stringify({ a: ['c', 'd'] }, { encodeValuesOnly: true, arrayFormat: 'comma' }), 'a=c,d');
+            s2t.equal(qs.stringify({ a: ['c', 'd'] }, { encodeValuesOnly: true }), 'a[0]=c&a[1]=d');
+
+            s2t.end();
+        });
 
         st.end();
     });
@@ -362,12 +379,12 @@ test('stringify()', function (t) {
         st.equal(qs.stringify({ a: [], b: [null], c: 'c' }, { encode: false, arrayFormat: 'indices' }), 'b[0]=&c=c');
         st.equal(qs.stringify({ a: [], b: [null], c: 'c' }, { encode: false, arrayFormat: 'brackets' }), 'b[]=&c=c');
         st.equal(qs.stringify({ a: [], b: [null], c: 'c' }, { encode: false, arrayFormat: 'repeat' }), 'b=&c=c');
-        st.equal(qs.stringify({ a: [], b: [null], c: 'c' }, { encode: false, arrayFormat: 'comma' }), 'b=&c=c');
+        st.equal(qs.stringify({ a: [], b: [null], c: 'c' }, { encode: false, arrayFormat: 'comma' }), 'b[]=&c=c');
         // with strictNullHandling
         st.equal(qs.stringify({ a: [], b: [null], c: 'c' }, { encode: false, arrayFormat: 'indices', strictNullHandling: true }), 'b[0]&c=c');
         st.equal(qs.stringify({ a: [], b: [null], c: 'c' }, { encode: false, arrayFormat: 'brackets', strictNullHandling: true }), 'b[]&c=c');
         st.equal(qs.stringify({ a: [], b: [null], c: 'c' }, { encode: false, arrayFormat: 'repeat', strictNullHandling: true }), 'b&c=c');
-        st.equal(qs.stringify({ a: [], b: [null], c: 'c' }, { encode: false, arrayFormat: 'comma', strictNullHandling: true }), 'b&c=c');
+        st.equal(qs.stringify({ a: [], b: [null], c: 'c' }, { encode: false, arrayFormat: 'comma', strictNullHandling: true }), 'b[]&c=c');
         // with skipNulls
         st.equal(qs.stringify({ a: [], b: [null], c: 'c' }, { encode: false, arrayFormat: 'indices', skipNulls: true }), 'c=c');
         st.equal(qs.stringify({ a: [], b: [null], c: 'c' }, { encode: false, arrayFormat: 'brackets', skipNulls: true }), 'c=c');
@@ -695,7 +712,7 @@ test('stringify()', function (t) {
                     arrayFormat: 'comma'
                 }
             ),
-            'a=' + date.getTime(),
+            'a%5B%5D=' + date.getTime(),
             'works with arrayFormat comma'
         );