Microsoft/TypeScript

Assignments to global objects in Javascript should be global declarations

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#22,446 opened on Mar 9, 2018

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 (3 comments) (0 reactions) (0 assignees)TypeScript (48,455 stars) (6,726 forks)batch import
BugDomain: JavaScriptEffort: ModerateExperience EnhancementHelp WantedRescheduled

Description

// @noEmit: true
// @allowJs: true
// @checkJs: true
// @Filename: a.js
global.x = 1
window.y = 2
this.z = 3

var n = x + y + z

Expected behavior: No error, and x, y and z are visible globally.

Actual behavior: Errors:

  1. Can't find name 'global'
  2. 'Window' has no property 'y'
  3. Cannot find name 'x', 'y' or 'z'

Ideally, global should only be visible when targetting node and window should only be visible when targetting the browser. It's not a requirement, though.

Contributor guide

Tech stack
typescriptjavascript
Domain
tooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
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
TypeScript basicsGlobal scope concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Investigate how the TypeScript compiler handles global assignments in .js files with checkJs enabled. Examine the type checker (src/compiler/checker.ts) to understand why 'global' is not recognized as a global object and why assignments to 'window' and 'this' are not treated as global declarations. Look at existing tests in tests/cases/... The issue provides a minimal reproduction; the fix likely involves updating the handling of global property assignments in JavaScript mode.