JS: introduce Expr::getUnderlyingReference

javascript/ql/src/semmle/javascript/Expr.qll

@@ -48,6 +48,13 @@ class ExprOrType extends @exprortype, Documentable {
   /** Gets this expression or type, with any surrounding parentheses removed. */
   ExprOrType stripParens() { result = this }
 
+  /**
+   * Gets the innermost reference that this expression evaluates to, if any.
+   */
+  Expr getUnderlyingReference() {
+    none()
+  }
+
   /**
    * Gets the innermost expression that this expression evaluates to.
    */
@@ -223,6 +230,10 @@ class ParExpr extends @parexpr, Expr {
     result = getExpression().getUnderlyingValue()
   }
 
+  override Expr getUnderlyingReference() {
+    result = getExpression().getUnderlyingReference()
+  }
+
 }
 
 /** A `null` literal. */
@@ -880,6 +891,11 @@ class PropAccess extends @propaccess, Expr {
   override ControlFlowNode getFirstControlFlowNode() {
     result = getBase().getFirstControlFlowNode()
   }
+
+  override Expr getUnderlyingReference() {
+    result = this
+  }
+
 }
 
 /** A dot expression. */

javascript/ql/src/semmle/javascript/TypeScript.qll

@@ -1320,6 +1320,10 @@ class TypeAssertion extends Expr, @typeassertion {
     result = getExpression().getUnderlyingValue()
   }
 
+  override Expr getUnderlyingReference() {
+    result = getExpression().getUnderlyingReference()
+  }
+
 }
 
 /**

javascript/ql/src/semmle/javascript/Variables.qll

@@ -298,6 +298,11 @@ class VarRef extends @varref, Identifier, BindingPattern, LexicalRef {
   override VarRef getABindingVarRef() { result = this }
 
   override predicate isImpure() { none() }
+
+  override Expr getUnderlyingReference() {
+    result = this
+  }
+
 }
 
 /** An identifier that refers to a variable in a non-declaring position. */