fixes #14: define required [[UnderlyingIterators]] internal slot

package.json

@@ -6,7 +6,7 @@
   "main": "lib/index.js",
   "scripts": {
     "build": "tsc",
-    "spec": "ecmarkup --mark-effects --load-biblio @tc39/ecma262-biblio --load-biblio ./proposal-iterator-helpers-biblio.json --write-biblio biblio.json --lint-spec --strict spec.emu --assets-dir dist dist/index.html",
+    "spec": "ecmarkup --mark-effects --load-biblio @tc39/ecma262-biblio --load-biblio ./proposal-iterator-helpers-biblio.json --load-biblio ./proposal-joint-iteration-biblio.json --write-biblio biblio.json --lint-spec --strict spec.emu --assets-dir dist dist/index.html",
     "test": "node --test test/index.mjs"
   },
   "repository": {

proposal-joint-iteration-biblio.json

@@ -0,0 +1 @@
+{"location":"https://tc39.es/proposal-joint-iteration/","entries":[{"type":"clause","id":"sec-iterator.zip","aoid":null,"title":"Iterator.zip ( iterables [ , options ] )","titleHTML":"Iterator.zip ( <var>iterables</var> [ , <var>options</var> ] )","number":"1"},{"type":"clause","id":"sec-iterator.zipkeyed","aoid":null,"title":"Iterator.zipKeyed ( iterables [ , options ] )","titleHTML":"Iterator.zipKeyed ( <var>iterables</var> [ , <var>options</var> ] )","number":"2"},{"type":"op","aoid":"IteratorZip","refId":"sec-IteratorZip","kind":"abstract operation","signature":{"parameters":[{"name":"_iters_","type":{"kind":"list","elements":{"kind":"opaque","type":"Iterator Records"}}},{"name":"_mode_","type":{"kind":"union","types":[{"kind":"opaque","type":"*\"shortest\"*"},{"kind":"opaque","type":"*\"longest\"*"},{"kind":"opaque","type":"*\"strict\"*"}]}},{"name":"_padding_","type":{"kind":"list","elements":{"kind":"opaque","type":"ECMAScript language values"}}},{"name":"_finishResults_","type":{"kind":"opaque","type":"an Abstract Closure that takes a List of ECMAScript values and returns an ECMAScript value"}}],"optionalParameters":[],"return":{"kind":"opaque","type":"a Generator"}},"effects":[]},{"type":"clause","id":"sec-IteratorZip","aoid":"IteratorZip","title":"IteratorZip ( iters, mode, padding, finishResults )","titleHTML":"IteratorZip ( <var>iters</var>, <var>mode</var>, <var>padding</var>, <var>finishResults</var> )","number":"3"},{"type":"op","aoid":"IteratorCloseAll","refId":"sec-closeall","kind":"abstract operation","signature":{"parameters":[{"name":"_iters_","type":{"kind":"list","elements":{"kind":"opaque","type":"Iterator Records"}}},{"name":"_completion_","type":{"kind":"completion","typeOfValueIfNormal":null,"completionType":"mixed"}}],"optionalParameters":[],"return":{"kind":"completion","typeOfValueIfNormal":null,"completionType":"mixed"}},"effects":["user-code"]},{"type":"clause","id":"sec-closeall","aoid":"IteratorCloseAll","title":"IteratorCloseAll ( iters, completion )","titleHTML":"IteratorCloseAll ( <var>iters</var>, <var>completion</var> )","number":"4"},{"type":"op","aoid":"IfAbruptCloseIterators","refId":"sec-ifabruptcloseiterators","signature":null,"effects":["user-code"]},{"type":"clause","id":"sec-ifabruptcloseiterators","aoid":"IfAbruptCloseIterators","title":"IfAbruptCloseIterators ( value, iteratorRecords )","titleHTML":"IfAbruptCloseIterators ( <var>value</var>, <var>iteratorRecords</var> )","number":"5"},{"type":"clause","id":"sec-%iteratorhelperprototype%.return","aoid":null,"title":"%IteratorHelperPrototype%.return ( )","titleHTML":"%IteratorHelperPrototype%.return ( )","number":"6"},{"type":"op","aoid":"GetOptionsObject","refId":"sec-getoptionsobject","kind":"abstract operation","signature":{"parameters":[{"name":"_options_","type":{"kind":"opaque","type":"an ECMAScript language value"}}],"optionalParameters":[],"return":{"kind":"completion","completionType":"mixed","typeOfValueIfNormal":{"kind":"opaque","type":"an Object"}}},"effects":[]},{"type":"clause","id":"sec-getoptionsobject","aoid":"GetOptionsObject","title":"GetOptionsObject ( options )","titleHTML":"GetOptionsObject ( <var>options</var> )","number":"7.1"},{"type":"clause","id":"stolen-infra","aoid":null,"title":"Infra","titleHTML":"Infra","number":"7"}]}

spec.emu

@@ -33,6 +33,8 @@ copyright: false
             1. If _completion_ is an abrupt completion, then
               1. Return ? IteratorClose(_iteratorRecord_, _completion_).
       1. Return ReturnCompletion(*undefined*).
-    1. Return CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%, « »).
+    1. Let _gen_ be CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%, « [[UnderlyingIterators]] »).
+    1. Set _gen_.[[UnderlyingIterators]] to a new empty List.
+    1. Return _gen_.
   </emu-alg>
 </emu-clause>