Allow chaining in map.set and set.add.

Author: mbostock

README.md

@@ -245,7 +245,6 @@ entries({foo: 42, bar: true}); // [{key: "foo", value: 42}, {key: "bar", value:
 Like [ES6 Maps](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map), but with a few differences:
 
 * Keys are coerced to strings.
-* [map.set](#map_set) returns the new value, not the map itself.
 * [map.each](#map_each), not [map.forEach](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/forEach). (Also, no *thisArg*.)
 * [map.remove](#map_remove), not [map.delete](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/delete).
 * [map.entries](#map_entries) returns an array of {key, value} objects, not an iterator of [key, value].
@@ -313,7 +312,6 @@ Returns the number of entries in this map.
 Like [ES6 Sets](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set), but with a few differences:
 
 * Values are coerced to strings.
-* [set.add](#set_add) returns the new value, not the set itself.
 * [set.each](#set_each), not [set.forEach](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/forEach). (Also, no *thisArg*.)
 * [set.remove](#set_remove), not [set.delete](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/delete).
 * [set.size](#set_size) is a method, not a [property](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/size); also, there’s [set.empty](#set_empty).

src/map.js

@@ -10,7 +10,8 @@ Map.prototype = map.prototype = {
     return this[prefix + key];
   },
   set: function(key, value) {
-    return this[prefix + key] = value;
+    this[prefix + key] = value;
+    return this;
   },
   remove: function(key) {
     var property = prefix + key;

src/set.js

@@ -9,7 +9,7 @@ Set.prototype = set.prototype = {
   add: function(value) {
     value += "";
     this[prefix + value] = true;
-    return value;
+    return this;
   },
   remove: proto.remove,
   clear: proto.clear,

test/map-test.js

@@ -305,9 +305,9 @@ tape("map.get(key) returns undefined for missing keys", function(test) {
   test.end()
 });
 
-tape("map.set(key, value) returns the set value", function(test) {
+tape("map.set(key, value) returns the map", function(test) {
   var m = arrays.map();
-  test.equal(m.set("foo", 42), 42);
+  test.equal(m.set("foo", 42), m);
   test.end();
 });
 

test/set-test.js

@@ -193,10 +193,10 @@ tape("set.has(value) returns undefined for missing values", function(test) {
   test.end();
 });
 
-tape("set.add(value) returns the set value, coerced to a string", function(test) {
+tape("set.add(value) returns the set", function(test) {
   var s = arrays.set();
-  test.equal(s.add("foo"), "foo");
-  test.strictEqual(s.add(2), "2");
+  test.equal(s.add("foo"), s);
+  test.equal(s.add(2), s);
   test.deepEqual(s.values().sort(), ["2", "foo"]);
   test.end();
 });