Implemented toJS in such a way that it only recurses into observables

src/api/tojs.ts

@@ -1,12 +1,63 @@
 import {isObservableArray} from "../types/observablearray";
+import {isObservableObject} from "../types/observableobject";
 import {isObservableMap} from "../types/observablemap";
 import {isObservableValue} from "../types/observablevalue";
+import {isObservable} from "../api/isobservable";
 import {deprecated} from "../utils/utils";
 
 /**
 	* Basically, a deep clone, so that no reactive property will exist anymore.
 	*/
 export function toJS(source, detectCycles: boolean = true, __alreadySeen: [any, any][] = null) {
+	// TODO: in 3.0, detectCycles should default to false?
+	// optimization: using ES6 map would be more efficient!
+	// optimization: lift this function outside toJS, this makes recursion expensive
+	function cache(value) {
+		if (detectCycles)
+			__alreadySeen.push([source, value]);
+		return value;
+	}
+	if (isObservable(source)) {
+		if (detectCycles && __alreadySeen === null)
+			__alreadySeen = [];
+		if (detectCycles && source !== null && typeof source === "object") {
+			for (let i = 0, l = __alreadySeen.length; i < l; i++)
+				if (__alreadySeen[i][0] === source)
+					return __alreadySeen[i][1];
+		}
+
+		if (isObservableArray(source)) {
+			const res = cache([]);
+			const toAdd = source.map(value => toJS(value, detectCycles, __alreadySeen));
+			res.length = toAdd.length;
+			for (let i = 0, l = toAdd.length; i < l; i++)
+				res[i] = toAdd[i];
+			return res;
+		}
+		if (isObservableObject(source)) {
+			const res = cache({});
+			for (let key in source)
+				res[key] = toJS(source[key], detectCycles, __alreadySeen);
+			return res;
+		}
+		if (isObservableMap(source)) {
+			const res = cache({});
+			source.forEach(
+				(value, key) => res[key] = toJS(value, detectCycles, __alreadySeen)
+			);
+			return res;
+		}
+		if (isObservableValue(source))
+			return toJS(source.get(), detectCycles, __alreadySeen);
+	}
+	return source;
+}
+
+/**
+	* Basically, a deep clone, so that no reactive property will exist anymore.
+	*/
+export function toJSlegacy(source, detectCycles: boolean = true, __alreadySeen: [any, any][] = null) {
+	deprecated("toJSlegacy is deprecated and will be removed in the next major. Use `toJS` instead. See #566");
 	// optimization: using ES6 map would be more efficient!
 	function cache(value) {
 		if (detectCycles)
@@ -28,7 +79,7 @@ export function toJS(source, detectCycles: boolean = true, __alreadySeen: [any,
 		return source;
 	if (Array.isArray(source) || isObservableArray(source)) {
 		const res = cache([]);
-		const toAdd = source.map(value => toJS(value, detectCycles, __alreadySeen));
+		const toAdd = source.map(value => toJSlegacy(value, detectCycles, __alreadySeen));
 		res.length = toAdd.length;
 		for (let i = 0, l = toAdd.length; i < l; i++)
 			res[i] = toAdd[i];
@@ -37,22 +88,22 @@ export function toJS(source, detectCycles: boolean = true, __alreadySeen: [any,
 	if (isObservableMap(source)) {
 		const res = cache({});
 		source.forEach(
-			(value, key) => res[key] = toJS(value, detectCycles, __alreadySeen)
+			(value, key) => res[key] = toJSlegacy(value, detectCycles, __alreadySeen)
 		);
 		return res;
 	}
 	if (isObservableValue(source))
-		return toJS(source.get(), detectCycles, __alreadySeen);
+		return toJSlegacy(source.get(), detectCycles, __alreadySeen);
 	if (typeof source === "object") {
 		const res = cache({});
 		for (let key in source)
-			res[key] = toJS(source[key], detectCycles, __alreadySeen);
+			res[key] = toJSlegacy(source[key], detectCycles, __alreadySeen);
 		return res;
 	}
 	return source;
 }
 
 export function toJSON(source, detectCycles: boolean = true, __alreadySeen: [any, any][] = null) {
 	deprecated("toJSON is deprecated. Use toJS instead");
-	return toJS.apply(null, arguments);
+	return toJSlegacy.apply(null, arguments);
 }

src/mobx.ts

@@ -48,7 +48,7 @@ export { autorun, autorunAsync, autorunUntil, when, reaction  } from "./api/auto
 export { action, isAction, runInAction                        } from "./api/action";
 
 export { expr                                                 } from "./api/expr";
-export { toJSON, toJS                                         } from "./api/tojs";
+export { toJSON, toJS, toJSlegacy                             } from "./api/tojs";
 export { ITransformer, createTransformer                      } from "./api/createtransformer";
 export { whyRun                                               } from "./api/whyrun";
 

test/api.js

@@ -39,13 +39,14 @@ test('correct api should be exposed', function(t) {
 		'runInAction',
 		'spy',
 		'toJS',
+		'toJSlegacy',
 		'toJSON',
 		'transaction',
 		'untracked',
 		'useStrict',
 		'when',
 		'whyRun'
-	]);
+	].sort());
 	t.equals(Object.keys(mobx).filter(function(key) {
 		return mobx[key] == undefined;
 	}).length, 0);