better key stringification

Author: Rich-Harris

src/stringify.js

@@ -4,6 +4,7 @@ import {
 	get_type,
 	is_plain_object,
 	is_primitive,
+	stringify_key,
 	stringify_string
 } from './utils.js';
 import {
@@ -154,7 +155,7 @@ export function stringify(value, reducers) {
 					if (Object.getPrototypeOf(thing) === null) {
 						str = '["null"';
 						for (const key in thing) {
-							keys.push(`.${key}`);
+							keys.push(stringify_key(key));
 							str += `,${stringify_string(key)},${flatten(thing[key])}`;
 							keys.pop();
 						}
@@ -165,7 +166,7 @@ export function stringify(value, reducers) {
 						for (const key in thing) {
 							if (started) str += ',';
 							started = true;
-							keys.push(`.${key}`);
+							keys.push(stringify_key(key));
 							str += `${stringify_string(key)}:${flatten(thing[key])}`;
 							keys.pop();
 						}

src/uneval.js

@@ -5,6 +5,7 @@ import {
 	get_type,
 	is_plain_object,
 	is_primitive,
+	stringify_key,
 	stringify_string
 } from './utils.js';
 
@@ -98,7 +99,7 @@ export function uneval(value, replacer) {
 					}
 
 					for (const key in thing) {
-						keys.push(`.${key}`);
+						keys.push(stringify_key(key));
 						walk(thing[key]);
 						keys.pop();
 					}

src/utils.js

@@ -104,3 +104,10 @@ export function enumerable_symbols(object) {
 		(symbol) => Object.getOwnPropertyDescriptor(object, symbol).enumerable
 	);
 }
+
+const is_identifier = /^[a-zA-Z_$][a-zA-Z_$0-9]*$/;
+
+/** @param {string} key */
+export function stringify_key(key) {
+	return is_identifier.test(key) ? '.' + key : '[' + JSON.stringify(key) + ']';
+}

test/test.js

@@ -584,13 +584,13 @@ for (const fn of [uneval, stringify]) {
 			class Whatever {}
 			fn({
 				foo: {
-					map: new Map([['key', new Whatever()]])
+					['string-key']: new Map([['key', new Whatever()]])
 				}
 			});
 		} catch (e) {
 			assert.equal(e.name, 'DevalueError');
 			assert.equal(e.message, 'Cannot stringify arbitrary non-POJOs');
-			assert.equal(e.path, '.foo.map.get("key")');
+			assert.equal(e.path, '.foo["string-key"].get("key")');
 		}
 	});