Use Map to internally represent contexts.

Author: dlongley

CHANGELOG.md

@@ -1,5 +1,11 @@
 # jsonld-signatures ChangeLog
 
+## 9.1.1 - 2021-06-xx
+
+### Fixed
+- Use `Map` to internally represent contexts instead of an object. This
+  optimizes better w/ v8.
+
 ## 9.1.0 - 2021-06-29
 
 ### Changed

lib/contexts.js

@@ -1,14 +1,14 @@
 /*
- * Copyright (c) 2017-2018 Digital Bazaar, Inc. All rights reserved.
+ * Copyright (c) 2017-2021 Digital Bazaar, Inc. All rights reserved.
  */
 'use strict';
 
 const constants = require('./constants');
 const {contexts: securityContexts} = require('security-context');
 
-module.exports = {
-  [constants.SECURITY_CONTEXT_V1_URL]:
-    securityContexts.get(constants.SECURITY_CONTEXT_V1_URL),
-  [constants.SECURITY_CONTEXT_V2_URL]:
-    securityContexts.get(constants.SECURITY_CONTEXT_V2_URL)
-};
+module.exports = new Map([
+  [constants.SECURITY_CONTEXT_V1_URL,
+    securityContexts.get(constants.SECURITY_CONTEXT_V1_URL)],
+  [constants.SECURITY_CONTEXT_V2_URL,
+    securityContexts.get(constants.SECURITY_CONTEXT_V2_URL)]
+]);

lib/documentLoader.js

@@ -1,5 +1,5 @@
 /*!
- * Copyright (c) 2018 Digital Bazaar, Inc. All rights reserved.
+ * Copyright (c) 2018-2021 Digital Bazaar, Inc. All rights reserved.
  */
 'use strict';
 
@@ -36,7 +36,7 @@ api.extendContextLoader = documentLoader => {
    * url then fetches a jsonld document.
    */
   return async url => {
-    const context = contexts[url];
+    const context = contexts.get(url);
     if(context !== undefined) {
       return {
         contextUrl: null,