Microsoft/TypeScript

Definite assignment assertion in JS not flagged

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#48,446 opened on Mar 27, 2022

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 (2 comments) (0 reactions) (0 assignees)TypeScript (6,726 forks)batch import
BugDomain: JavaScriptHelp Wanted

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Description

Bug Report

Noted by someone on Discord.

🔎 Search Terms

non null assertion javascript error

Related https://github.com/microsoft/TypeScript/issues/17222

🕗 Version & Regression Information

  • This is the behavior in every version I tried

⏯ Playground Link

Playground link with relevant code

💻 Code

const a = { a!: 1 };

🙁 Actual behavior

There's no error; crashes at runtime

🙂 Expected behavior

There should be an error

Contributor guide

Research direction
Inspect the parser or type checker to find where definite assignment assertions are allowed. Add a check for file extension (.js vs .ts) to emit an error in JavaScript files.
Tech stack
typescriptjavascript
Domain
developer experience
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.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
TypeScriptJavaScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65