Fix more possible 'in' vs 'hasOwnProperty' bugs.

Author: davidlehn

lib/context.js

@@ -293,7 +293,8 @@ api.createTermDefinition = (
   }
 
   // FIXME if(1.1) ... ?
-  if(term in activeCtx.protected && !isPropertyTermScopedContext) {
+  if(activeCtx.protected.hasOwnProperty(term) &&
+    !isPropertyTermScopedContext) {
     const protectedMode = (options && options.protectedMode) || 'error';
     if(protectedMode === 'error') {
       throw new JsonLdError(
@@ -435,7 +436,7 @@ api.createTermDefinition = (
     // see if the term has a prefix
     if(mapping._termHasColon) {
       const prefix = term.substr(0, colon);
-      if(prefix in localCtx) {
+      if(localCtx.hasOwnProperty(prefix)) {
         // define parent prefix
         api.createTermDefinition(activeCtx, localCtx, prefix, defined, options);
       }
@@ -711,7 +712,7 @@ function _expandIri(activeCtx, value, relativeTo, localCtx, defined, options) {
     }
 
     // prefix dependency not defined, define it
-    if(localCtx && prefix in localCtx) {
+    if(localCtx && localCtx.hasOwnProperty(prefix)) {
       api.createTermDefinition(activeCtx, localCtx, prefix, defined, options);
     }
 
@@ -918,7 +919,7 @@ api.getInitialContext = options => {
    * @param typeOrLanguageValue the key in the entry to add to.
    */
   function _addPreferredTerm(term, entry, typeOrLanguageValue) {
-    if(!(typeOrLanguageValue in entry)) {
+    if(!entry.hasOwnProperty(typeOrLanguageValue)) {
       entry[typeOrLanguageValue] = term;
     }
   }
@@ -974,14 +975,14 @@ api.getContextValue = (ctx, key, type) => {
       // return whole entry
       return entry;
     }
-    if(type in entry) {
+    if(entry.hasOwnProperty(type)) {
       // return entry value for type
       return entry[type];
     }
   }
 
   // get default language
-  if(type === '@language' && (type in ctx)) {
+  if(type === '@language' && ctx.hasOwnProperty(type)) {
     return ctx[type];
   }