Microsoft/TypeScript

Comment like jsx text emitted twice when preserve enabled

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#61860 opened on Jun 13, 2025

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BugDomain: JSX/TSXHelp Wanted

Description

🔎 Search Terms

comment like jsx text, preserve jsx

🕗 Version & Regression Information

  • This is the behavior in every version I tried, and I reviewed the FAQ for entries about _________

⏯ Playground Link

https://www.typescriptlang.org/play/?jsx=1#code/GYVwdgxgLglg9mABAQQA6oBQEpEG8C+AUMRAgM5SIBWZAHogLyIA8aqAfAPQBUiYcibp1w9EARkGdxAJgDMiUdMn5R-Sc05t2AbkJA

💻 Code

function App() {}
const jsx = <App>/* no */{/* 1 */ 123 /* 2 */}/* no */</App>;

🙁 Actual behavior

These duplicate sections will be rendered in the JSX text output:

"use strict";
function App() { }
const jsx = <App> /* no *//* no */{/* 1 */123 /* 2 */} /* no *//* no */</App>
//                ~~~~~~~                              ~~~~~~~

🙂 Expected behavior

"use strict";
function App() { }
- const jsx = <App> /* no *//* no */{/* 1 */123 /* 2 */} /* no *//* no */</App>
+ const jsx = <App> /* no */{/* 1 */123 /* 2 */} /* no */</App>

Additional information about the issue

No response

Contributor guide

Tech stack
typescriptreact
Domain
tooling
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.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
basic understanding of JSXTypeScript compiler architecture
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Start by reading the TypeScript compiler source, specifically the JSX emitter logic in 'src/compiler/emitter.ts'. Look for how text nodes inside JSX are handled when 'jsx: preserve' is set. The issue shows that text before and after expression braces is emitted twice. The fix likely involves deduplicating text emission for JSX children. The playground link (https://www.typescriptlang.org/play/?jsx=1#code=...) reproduces the bug. Check for existing comments or PRs linked to issue #61860; as of now there are none. Confirm the expected behavior by comparing the actual output with the diff provided.