[js] Implement nqp::getlexcaller.

Author: pmurias

src/vm/js/Operations.nqp

@@ -1292,6 +1292,7 @@ class QAST::OperationsJS {
     }
 
     add_simple_op('getlexdyn', $T_OBJ, [$T_STR], sub ($name) {"{$*CTX}.lookupDynamicFromCaller($name)"});
+    add_simple_op('getlexcaller', $T_OBJ, [$T_STR], sub ($name) {"{$*CTX}.lookupFromSomeCaller($name)"});
     add_simple_op('getlexrel', $T_OBJ, [$T_OBJ, $T_STR]);
 
     add_simple_op('captureexistsnamed', $T_INT, [$T_OBJ, $T_STR]);

src/vm/js/nqp-runtime/runtime.js

@@ -272,6 +272,21 @@ Ctx.prototype.lookupDynamicFromCaller = function(name) {
      nqp code usually fallbacks to looking up of global */
 };
 
+Ctx.prototype.lookupFromSomeCaller = function(name) {
+  var currentCallerCtx = this.caller;
+  while (currentCallerCtx) {
+    var currentCtx = currentCallerCtx;
+    while (currentCtx) {
+      if (currentCtx.hasOwnProperty(name)) {
+        return currentCtx[name];
+      }
+      currentCtx = currentCtx.outer;
+    }
+    currentCallerCtx = currentCallerCtx.caller;
+  }
+  return null;
+};
+
 Ctx.prototype.lookup = function(name) {
   var ctx = this;
   while (ctx) {