[New] parse/stringify: Pass extra key/value argument to decoder

A new fourth argument is now provided when invoking the decoder inside parse,
this argument represents whether the first argument (str) is a key or a value.
This can then be used to decode key and values different within the decode function.

A test has been added for this new behavior.

README.md

@@ -330,6 +330,30 @@ var decoded = qs.parse('x=z', { decoder: function (str) {
 }})
 ```
 
+You can encode keys and values using different logic by using the type argument provided to the encoder:
+
+```javascript
+var encoded = qs.stringify({ a: { b: 'c' } }, { encoder: function (str, defaultEncoder, charset, type) {
+    if (type === 'key') {
+        return // Encoded key
+    } else if (type === 'value') {
+        return // Encoded value
+    }
+}})
+```
+
+The type argument is also provided to the decoder:
+
+```javascript
+var decoded = qs.parse('x=z', { decoder: function (str, defaultEncoder, charset, type) {
+    if (type === 'key') {
+        return // Decoded key
+    } else if (type === 'value') {
+        return // Decoded value
+    }
+}})
+```
+
 Examples beyond this point will be shown as though the output is not URI encoded for clarity. Please note that the return values in these cases *will* be URI encoded during real usage.
 
 When arrays are stringified, by default they are given explicit indices:

lib/parse.js

@@ -72,11 +72,11 @@ var parseValues = function parseQueryStringValues(str, options) {
 
         var key, val;
         if (pos === -1) {
-            key = options.decoder(part, defaults.decoder, charset);
+            key = options.decoder(part, defaults.decoder, charset, 'key');
             val = options.strictNullHandling ? null : '';
         } else {
-            key = options.decoder(part.slice(0, pos), defaults.decoder, charset);
-            val = options.decoder(part.slice(pos + 1), defaults.decoder, charset);
+            key = options.decoder(part.slice(0, pos), defaults.decoder, charset, 'key');
+            val = options.decoder(part.slice(pos + 1), defaults.decoder, charset, 'value');
         }
 
         if (val && options.interpretNumericEntities && charset === 'iso-8859-1') {

lib/stringify.js

@@ -80,16 +80,16 @@ var stringify = function stringify( // eslint-disable-line func-name-matching
 
     if (obj === null) {
         if (strictNullHandling) {
-            return encoder && !encodeValuesOnly ? encoder(prefix, defaults.encoder, charset) : prefix;
+            return encoder && !encodeValuesOnly ? encoder(prefix, defaults.encoder, charset, 'key') : prefix;
         }
 
         obj = '';
     }
 
     if (isNonNullishPrimitive(obj) || utils.isBuffer(obj)) {
         if (encoder) {
-            var keyValue = encodeValuesOnly ? prefix : encoder(prefix, defaults.encoder, charset);
-            return [formatter(keyValue) + '=' + formatter(encoder(obj, defaults.encoder, charset))];
+            var keyValue = encodeValuesOnly ? prefix : encoder(prefix, defaults.encoder, charset, 'key');
+            return [formatter(keyValue) + '=' + formatter(encoder(obj, defaults.encoder, charset, 'value'))];
         }
         return [formatter(prefix) + '=' + formatter(String(obj))];
     }

test/.eslintrc

@@ -11,7 +11,8 @@
         "no-buffer-constructor": 0,
         "no-extend-native": 0,
         "no-magic-numbers": 0,
+        "no-throw-literal": 0,
         "object-curly-newline": 0,
-        "sort-keys": 0
+        "sort-keys": 0,
     }
 }

test/parse.js

@@ -686,5 +686,20 @@ test('parse()', function (t) {
         st.end();
     });
 
+    t.test('allows for decoding keys and values differently', function (st) {
+        var decoder = function (str, defaultDecoder, charset, type) {
+            if (type === 'key') {
+                return defaultDecoder(str, defaultDecoder, charset, type).toLowerCase();
+            }
+            if (type === 'value') {
+                return defaultDecoder(str, defaultDecoder, charset, type).toUpperCase();
+            }
+            throw 'this should never happen! type: ' + type;
+        };
+
+        st.deepEqual(qs.parse('KeY=vAlUe', { decoder: decoder }), { key: 'VALUE' });
+        st.end();
+    });
+
     t.end();
 });

test/stringify.js

@@ -719,5 +719,20 @@ test('stringify()', function (t) {
         st.end();
     });
 
+    t.test('allows for encoding keys and values differently', function (st) {
+        var encoder = function (str, defaultEncoder, charset, type) {
+            if (type === 'key') {
+                return defaultEncoder(str, defaultEncoder, charset, type).toLowerCase();
+            }
+            if (type === 'value') {
+                return defaultEncoder(str, defaultEncoder, charset, type).toUpperCase();
+            }
+            throw 'this should never happen! type: ' + type;
+        };
+
+        st.deepEqual(qs.stringify({ KeY: 'vAlUe' }, { encoder: encoder }), 'key=VALUE');
+        st.end();
+    });
+
     t.end();
 });