JS: Expose content-based accessors

Author: asgerf

javascript/ql/lib/semmle/javascript/ApiGraphs.qll

@@ -230,22 +230,33 @@ module API {
     }
 
     /**
-     * Gets a node representing an arbitrary array element in the array represented by this node.
+     * Gets a representative for the `content` of this value.
+     *
+     * When possible, it is preferrable to use one of the specialized variants of this predicate, such as `getMember`.
      */
     cached
-    Node getArrayElement() {
-      exists(string s, int n |
-        result = this.getMember(s) and
-        s.toInt() = n and
-        n.toString() = s and // ensure 's' is the canonical integer representation
-        n >= 0
-      )
-      or
-      result = this.getMember(DataFlow::PseudoProperties::arrayElement())
-      or
-      result = this.getUnknownMember()
+    Node getContent(DataFlow::Content content) {
+      // This predicate is currently not 'inline_late' because 'content' can be an input or output
+      Stages::ApiStage::ref() and
+      result = this.getASuccessor(Label::content(content))
     }
 
+    /**
+     * Gets a representative for the `contents` of this value.
+     */
+    bindingset[this, contents]
+    pragma[inline_late]
+    Node getContents(DataFlow::ContentSet contents) {
+      // We always use getAStoreContent when generating content edges, and we always use getAReadContent when querying the graph.
+      result = this.getContent(contents.getAReadContent())
+    }
+
+    /**
+     * Gets a node representing an arbitrary array element in the array represented by this node.
+     */
+    cached
+    Node getArrayElement() { result = this.getContents(DataFlow::ContentSet::arrayElement()) }
+
     /**
      * Gets a node representing a member of this API component where the name of the member may
      * or may not be known statically.