facebookarchive/prepack

Prepack emits code containing invalid global.TypedArray access

Open

#2292 opened on Jul 18, 2018

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Description

TypedArray is a global not exposed to the user JavaScript runtime. Try global.TypedArray in your JavaScript environment of choice. We must emit Object.getPrototypeOf(Int8Array) or similar instead of TypedArray.

Input

var TypedArray = Object.getPrototypeOf(Int8Array);
console.log(TypedArray.from.name === "from");

Output

var TypedArray;
(function() {
  var _$0 = this;

  var _$1 = _$0.TypedArray; // <-------------------- `TypedArray` is not exposed on the global object!
  _$0.TypedArray = _$1;
  console.log(true);
}.call(this));

Contributor guide

Tech stack
javascriptnodejs
Domain
build system
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Understanding of JavaScript prototypesFamiliarity with Prepack's code generation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
The issue is that Prepack incorrectly emits `global.TypedArray` instead of a valid expression like `Object.getPrototypeOf(Int8Array)`. To fix, locate where Prepack serializes global object property accesses and replace the usage of `TypedArray` with a reference that works in all JavaScript environments. The relevant code is likely in the serializer or environment module of Prepack. Check the source files in the `lib/` directory for handling of built in objects. The fix should ensure that the emitted code does not assume `TypedArray` is a global.