WIP: Make observable map structurally match an ES6 Map

src/types/observablemap.ts

@@ -11,7 +11,8 @@ import {
     deprecated,
     isES6Map,
     getMapLikeKeys,
-    fail
+    fail,
+    declareStringTag
 } from "../utils/utils"
 import {
     IInterceptable,
@@ -40,9 +41,18 @@ export interface IMap<K, V> {
     get(key: K): V | undefined
     has(key: K): boolean
     set(key: K, value?: V): this
+    [Symbol.toStringTag]: "Map"
+    [Symbol.iterator](): IterableIterator<[K, V]>
+    entries(): IterableIterator<[K, V]>
+    keys(): IterableIterator<K>
+    values(): IterableIterator<V>
     readonly size: number
 }
 
+export interface IterableIterator<T> extends Iterator<T> {
+    [Symbol.iterator](): IterableIterator<T>
+}
+
 export interface IKeyValueMap<V> {
     [key: string]: V
 }
@@ -376,10 +386,20 @@ export class ObservableMap<V>
     }
 }
 
+/**
+ * Include the interface to cover the implementations added to the prototype directly.
+ */
+export interface ObservableMap<V> {
+    [Symbol.toStringTag]: "Map"
+    [Symbol.iterator](): IterableIterator<[string, V]>
+}
+
 declareIterator(ObservableMap.prototype, function() {
     return this.entries()
 })
 
+declareStringTag(ObservableMap.prototype, "Map")
+
 export function map<V>(initialValues?: IObservableMapInitialValues<V>): ObservableMap<V> {
     deprecated("`mobx.map` is deprecated, use `new ObservableMap` or `mobx.observable.map` instead")
     return observable.map<V>(initialValues)

src/utils/iterable.ts

@@ -10,11 +10,15 @@ function iteratorSymbol() {
 
 export const IS_ITERATING_MARKER = "__$$iterating"
 
+export interface IteratorResult<T> {
+    done: boolean
+    value: T
+}
+
 export interface Iterator<T> {
-    next(): {
-        done: boolean
-        value?: T
-    }
+    next(value?: any): IteratorResult<T>
+    return?(value?: any): IteratorResult<T>
+    throw?(e?: any): IteratorResult<T>
 }
 
 export function arrayAsIterator<T>(array: T[]): T[] & Iterator<T> {

src/utils/utils.ts

@@ -192,6 +192,12 @@ export function toPrimitive(value) {
     return value === null ? null : typeof value === "object" ? "" + value : value
 }
 
+const stringTagSymbol = (typeof Symbol === "function" && Symbol.toStringTag) || "@@toStringTag"
+
+export function declareStringTag<T>(prototType, tag: string) {
+    addHiddenFinalProp(prototType, stringTagSymbol, tag)
+}
+
 import { globalState } from "../core/globalstate"
 import { IObservableArray, isObservableArray } from "../types/observablearray"
 import { isObservableMap, ObservableMap, IKeyValueMap } from "../types/observablemap"

test/base/map.js

@@ -642,3 +642,9 @@ test("#1258 cannot replace maps anymore", () => {
     const items = mobx.observable.map()
     items.replace(mobx.observable.map())
 })
+
+test("map should implement toStringTag", () => {
+    const m = mobx.observable.map({ a: 1 })
+    const name = Object.prototype.toString.call(m)
+    expect(name).toBe("[object Map]")
+})

test/base/typescript-tests.ts

@@ -1247,3 +1247,8 @@ test("1072 - @observable without initial value and observe before first access",
     const user = new User()
     observe(user, "loginCount", () => {})
 })
+
+test("map should structurally match ES6 Map", () => {
+    // Including this line strictly for type checking.
+    const m: Map<string, number> = mobx.observable.map({ a: 1, b: 2 })
+})

test/tsconfig.json

@@ -4,6 +4,9 @@
         "target": "es5",
         "noImplicitAny": true,
         "sourceMap": false,
-		"experimentalDecorators": true
+		"experimentalDecorators": true,
+        "lib": [
+          "es2015"
+        ]
     }
 }

tsconfig.json

@@ -13,7 +13,7 @@
         "noImplicitAny": false,
         "moduleResolution": "node",
         "lib": [
-            "es5",
+            "es2015",
             "dom"
         ]
     },