dict: Make set method return value consistent with Map.

Signed-off-by: Anders Kaseorg <anders@zulipchat.com>

frontend_tests/node_tests/dict.js

@@ -36,7 +36,7 @@ run_test('basic', () => {
 
     const val = ['foo'];
     const res = d.set('abc', val);
-    assert.equal(val, res);
+    assert.strictEqual(res, d);
 });
 
 run_test('undefined_keys', () => {

frontend_tests/node_tests/fold_dict.js

@@ -36,7 +36,7 @@ run_test('basic', () => {
 
     const val = ['foo'];
     const res = d.set('abc', val);
-    assert.equal(val, res);
+    assert.strictEqual(res, d);
 });
 
 run_test('case insensitivity', () => {

frontend_tests/node_tests/int_dict.js

@@ -35,7 +35,7 @@ run_test('basic', () => {
 
     const val = ['fred'];
     const res = d.set(103, val);
-    assert.equal(val, res);
+    assert.strictEqual(res, d);
 });
 
 

static/js/dict.ts

@@ -5,9 +5,9 @@ export class Dict<V> {
         return this._items.get(this._munge(key));
     }
 
-    set(key: string, value: V): V {
+    set(key: string, value: V): Dict<V> {
         this._items.set(this._munge(key), value);
-        return value;
+        return this;
     }
 
     has(key: string): boolean {

static/js/fold_dict.ts

@@ -25,9 +25,9 @@ export class FoldDict<V> {
         return mapping.v;
     }
 
-    set(key: string, value: V): V {
+    set(key: string, value: V): FoldDict<V> {
         this._items.set(this._munge(key), {k: key, v: value});
-        return value;
+        return this;
     }
 
     has(key: string): boolean {

static/js/int_dict.ts

@@ -26,10 +26,10 @@ export class IntDict<V> {
         return this._map.get(key);
     }
 
-    set(key: number, value: V): V {
+    set(key: number, value: V): IntDict<V> {
         key = this._convert(key);
         this._map.set(key, value);
-        return value;
+        return this;
     }
 
     has(key: number): boolean {