Use Map for tracking URLs.

Author: dlongley

lib/context.js

@@ -946,7 +946,6 @@ async function _retrieveContextUrls(input, options) {
   const documentLoader = util.normalizeDocumentLoader(options.documentLoader);
 
   // retrieve all @context URLs in input
-  const _urls = {};
   await retrieve(input, {}, documentLoader);
 
   return input;
@@ -960,17 +959,12 @@ async function _retrieveContextUrls(input, options) {
         {code: 'loading remote context failed', max: MAX_CONTEXT_URLS});
     }
 
-    // find all URLs in the given document, reusing already retrieved URLs
-    const urls = {};
-    Object.keys(_urls).forEach(url => {
-      if(_urls[url] !== false) {
-        urls[url] = _urls[url];
-      }
-    });
+    // find all URLs in the given document
+    const urls = new Map();
     _findContextUrls(doc, urls, false, options.base);
 
     // queue all unretrieved URLs
-    const queue = Object.keys(urls).filter(u => urls[u] === false);
+    const queue = [...urls.keys()].filter(u => urls.get(u) === false);
 
     // retrieve URLs in queue
     return Promise.all(queue.map(async url => {
@@ -979,7 +973,7 @@ async function _retrieveContextUrls(input, options) {
         throw new JsonLdError(
           'Cyclical @context URLs detected.',
           'jsonld.ContextUrlError',
-          {code: 'recursive context inclusion', url: url});
+          {code: 'recursive context inclusion', url});
       }
 
       const _cycles = util.clone(cycles);
@@ -1003,7 +997,7 @@ async function _retrieveContextUrls(input, options) {
           'non-JSON response, or more than one HTTP Link Header was ' +
           'provided for a remote context.',
           'jsonld.InvalidUrl',
-          {code: 'loading remote context failed', url: url, cause: e});
+          {code: 'loading remote context failed', url, cause: e});
       }
 
       // ensure ctx is an object
@@ -1012,7 +1006,7 @@ async function _retrieveContextUrls(input, options) {
           'Dereferencing a URL did not result in a JSON object. The ' +
           'response was valid JSON, but it was not a JSON object.',
           'jsonld.InvalidUrl',
-          {code: 'invalid remote context', url: url});
+          {code: 'invalid remote context', url});
       }
 
       // use empty context if no @context key is present
@@ -1034,7 +1028,7 @@ async function _retrieveContextUrls(input, options) {
       await retrieve(ctx, _cycles, documentLoader);
 
       // store retrieved context w/replaced @context URLs
-      urls[url] = ctx['@context'];
+      urls.set(url, ctx['@context']);
 
       // replace all @context URLs in the document
       _findContextUrls(doc, urls, true, options.base);
@@ -1083,7 +1077,7 @@ function _findContextUrls(input, urls, replace, base) {
         const _ctx = ctx[i];
         if(_isString(_ctx)) {
           const prepended = prependBase(base, _ctx);
-          const resolved = urls[prepended];
+          const resolved = urls.get(prepended);
           // replace w/@context if requested
           if(replace) {
             if(_isArray(resolved)) {
@@ -1096,7 +1090,7 @@ function _findContextUrls(input, urls, replace, base) {
             }
           } else if(resolved === undefined) {
             // @context URL found
-            urls[prepended] = false;
+            urls.set(prepended, false);
           }
         } else {
           // look for scoped context
@@ -1110,15 +1104,15 @@ function _findContextUrls(input, urls, replace, base) {
     } else if(_isString(ctx)) {
       // string @context
       const prepended = prependBase(base, ctx);
-      const resolved = urls[prepended];
+      const resolved = urls.get(prepended);
       // replace w/@context if requested
       if(replace) {
         if(resolved !== false) {
           input[key] = resolved;
         }
       } else if(resolved === undefined) {
         // @context URL found
-        urls[prepended] = false;
+        urls.set(prepended, false);
       }
     } else {
       // look for scoped context