microsoft / microsoft/TypeScript

compilerOptions support TDZ error option

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#33,576 3 comments 0 reactions 0 assignees View on GitHub

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Description

According to the PR of #32221 , to prevent such problem like:

(function () {
    function cleanup() {
        console.log(A); // throw error
    }

    cleanup();
    const A = 1;
}());

this snippet will compile into:

(function () {
    function cleanup() {
        console.log(A); // log undefined
    }
    cleanup();
    var A = 1;
}());

Error in the first snippet will be ignored, and cause TDZ error. Can tsc support TDZ error enabled option like babel-plugin-transform-block-scoping ? It will notify peoples who write such pattern to prevent further weird problems.

Checklist

My suggestion meets these guidelines:

  • This wouldn't be a breaking change in existing TypeScript/JavaScript code
  • This wouldn't change the runtime behavior of existing JavaScript code
  • This could be implemented without emitting different JS based on the types of the expressions
  • This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
  • This feature would agree with the rest of TypeScript's Design Goals.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reading the issue's TypeScript and JavaScript examples and the referenced PR #32221. Clarify how a compiler option should report temporal dead zone patterns and what diagnostics it should produce; done means the proposed option is defined well enough to implement and validate without changing existing output by default.

Written by the indexing model from the issue text.

Assessment

Tech stack
javascript, typescript
Domain
compilers
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
25/100

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