Microsoft/TypeScript

Template string downlevel to ES5 escapes more Unicode characters than necessary

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#10,498 opened on Aug 23, 2016

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 (5 comments) (8 reactions) (0 assignees)TypeScript (48,455 stars) (6,726 forks)batch import
Experience EnhancementHelp WantedSuggestion

Description

TypeScript Version: 1.8.10

Typescript compiles template strings with Unicode characters incorrectly.

Code

var test1: string = 'test'; // Normal string (only English)
var test2: string = `test`; // Template string (only English)
var test3: string = 'тест'; // Normal string (Cyrillic)
var test4: string = `тест`; // Template string (Cyrillic)

Expected behavior:

There should be no significant difference in string representation, no matter language they are using. Since this is Unicode anyway. You can see expected behavior on standard, singleline strings. This behavior I would consider normal, expected.

var test1 = 'test'; // Normal string (only English)
var test2 = "test"; // Template string (only English)
var test3 = 'тест'; // Normal string (Cyrillic)
var test4 = "тест"; // Template string (Cyrillic)

Actual behavior:

Multiline (template) strings with none-English characters becomes encoded.

var test1 = 'test'; // Normal string (only English)
var test2 = "test"; // Template string (only English)
var test3 = 'тест'; // Normal string (Cyrillic)
var test4 = "\u0442\u0435\u0441\u0442"; // Template string (Cyrillic)

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Contributor guide

Tech stack
typescriptjavascript
Domain
toolingdeveloper 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.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
TypeScript basicsUnicode escaping
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75
Research direction
Examine the TypeScript emitter code in `src/compiler/emitter.ts` where template strings are downleveled. Specifically, look for the logic that converts Unicode characters in template strings to escape sequences. The issue is that non ASCII characters like Cyrillic are being escaped unnecessarily when within template strings but not in regular strings. The fix should align the behavior of template strings with regular strings during ES5 downlevel compilation.