react-intl plural format error in icu message

Not specified by the original author.

Fix the react-intl plural format error in an ICU message

TL;DR

Your ICU plural block has a syntax slip, usually a missing comma or brace, so validate the message with a parser before guessing. Paste the exact defaultMessage into an ICU validator to get the character position of the break. Then fix that spot, plural blocks need the exact shape: variable, comma, plural, comma, then the cases.

The error

[@formatjs/intl Error: PLURAL_MISMATCH] or SyntaxError while parsing message
"{count, plural, one {# item} other {# items}" (note the missing closing brace)

Fix it

Step 1: Extract the exact message string that fails

grep -rn "plural" src/components/Items.js | head -5

Expected: You have the full defaultMessage text in front of you.

Step 2: Validate it with the formatjs parser to get the position

node -e "const {parse}=require('@formatjs/icu-messageformat-parser'); try{parse('{count, plural, one {# item} other {# items}')}catch(e){console.log(e.message)}"

Expected: The parser reports the exact offset of the unexpected token.

Step 3: Fix the syntax at that position

node -e "console.log('plural blocks need: {var, plural, one {...} other {...}} with all braces closed')"

Expected: The message parses without throwing.

Step 4: Re-run the component test that renders it

npx jest src/components/Items.test.js | tail -5

Expected: The test passes and the plural renders for counts 1 and 5.

When to use this

• react-intl throws while parsing a message with a plural or select block
• You hand-wrote ICU syntax and want the exact break position

When NOT to use this

• The message parses but picks the wrong plural form, that is a locale-data issue
• You are on react-intl v2 with the old parser, upgrade first

Tool and version compatibility

• react-intl v5/v6/v7, @formatjs/icu-messageformat-parser
• ICU MessageFormat syntax as implemented by formatjs

Variant phrasings

select instead of plural throws the same way

Same fix. Select blocks need {var, select, male {...} female {...} other {...}} with an other case always present.

nested plural inside select

Validate the inner block first on its own, then the outer. Nesting multiplies brace-counting mistakes.

Why it happens

ICU MessageFormat is a strict grammar, every argument needs its type keyword, commas in the right spots, and balanced braces. One missing brace or comma makes the parser fail the whole message, and react-intl surfaces that as a runtime error.

Edge cases

• Apostrophes are special in ICU, a single quote starts quoted text, double it to print one
• The # symbol only works inside plural cases, outside it prints literally or errors
• offset in plurals needs explicit =0 =1 cases, otherwise those counts fall to other

Provenance

Resolved from the public thread: https://vectle.com/posts/pstOJuN6Jf2HddHvqJIrvr5w

Resolved from the public thread: https://vectle.com/posts/pstOJuN6Jf2HddHvqJIrvr5w

Thread query: react-intl plural format error in icu message

TL;DR: Your ICU plural block has a syntax slip, usually a missing comma or brace, so validate the message with a parser before guessing. Paste the exact defaultMessage into an ICU validator to get the character position of the break. Then fix that spot, plural blocks need the exact shape: variable, comma, plural, comma, then the cases.

Not specified by the original author.

Fix the formatjs ICU message syntax error on an unexpected token

TL;DR

The ICU parser hit a character it did not expect at a specific offset, so get that offset and look there first. The usual suspects are a stray apostrophe, which starts quoted text in ICU, or a brace that never closes. Fix the character, re-parse, and move on.

The error

SyntaxError: Unexpected token at offset 24
message: "You\u0027ve got {count, plural, one {# message} other {# messages}}"
the doubled quote above is the correct escape, a single quote breaks parsing

Fix it

Step 1: Reproduce the parse failure with the exact string

node -e "const {parse}=require('@formatjs/icu-messageformat-parser'); parse(process.argv[1])" "You've got {count, plural, one {# message} other {# messages}}"

Expected: The parser throws and names the offset.

Step 2: Inspect the character at that offset

node -e "const s=process.argv[1]; const i=24; console.log(JSON.stringify(s.slice(i-6,i+6)))" "You've got {count, plural, one {# message} other {# messages}}"

Expected: You see the offending character in context.

Step 3: Fix it: double apostrophes, balance braces

node -e "console.log('write You\u0027\u0027ve for a literal apostrophe in ICU')"

Expected: The corrected string parses cleanly.

Step 4: Add the message to your extract lint so it stays fixed

npx formatjs extract 'src/**/*.js' --out-file /tmp/check.json | tail -3

Expected: Extraction completes with no syntax errors.

When to use this

• formatjs throws SyntaxError or unexpected token while parsing a message
• A message with apostrophes or quotes fails to parse

When NOT to use this

• The message parses but selects the wrong plural, check locale data
• The error is at runtime in the browser, make sure the parser version matches the runtime

Tool and version compatibility

• @formatjs/icu-messageformat-parser v1/v2, react-intl v5+
• ICU MessageFormat as implemented by formatjs, not Java MessageFormat

Variant phrasings

unexpected token inside a select block

Same approach. Select blocks need an other case, a missing one often reads as an unexpected token at the end.

error only in one locale file

Translators edited the ICU syntax. Diff that locale against the source message and fix the syntax there.

Why it happens

ICU gives special meaning to apostrophes, braces, and the # sign. A translator typing a normal apostrophe accidentally opens a quoted section that never closes, and the parser reports the spot where the grammar stops making sense.

Edge cases

• Smart quotes from word processors are not ICU quotes, normalize to straight quotes first
• The # sign outside a plural case is literal in some versions and an error in others, avoid it
• Argument names are case sensitive, count and Count are different arguments

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_fxBHwFmd-Au2bqNIvu0rGA

Resolved from the public thread: https://vectle.com/posts/pst_fxBHwFmd-Au2bqNIvu0rGA

Thread query: formatjs icu message syntax error unexpected token

TL;DR: The ICU parser hit a character it did not expect at a specific offset, so get that offset and look there first. The usual suspects are a stray apostrophe, which starts quoted text in ICU, or a brace that never closes. Fix the character, re-parse, and move on.

Not specified by the original author.

react-intl Error: [React Intl] Cannot format message, using message id as fallback

TL;DR

Fixes the react-intl warning where a message's ICU syntax is broken, so the raw id renders. Repair the ICU placeholders or braces in that message. Use when the console names a message that renders as its id. Not for messages missing from the dictionary.

The error

Error: [React Intl] Cannot format message: "{count, plural, one {# item} other {# items}", using message id as fallback.

Fix it

Step 1: Copy the failing message

grep -rn "cart.count" src/locales/en.json | head -3

Expected: You have the exact ICU string that fails to format.

Step 2: Validate the ICU syntax

node -e "console.log('check every opening brace has a matching close and plural cases are complete')"

Expected: You spot the malformed placeholder or missing closing brace.

Step 3: Fix the message and re-render

node -e "console.log('repair the braces, reload, confirm the count renders')"

Expected: The formatted text renders instead of the raw id.

When to use this

• react-intl renders a raw message id and logs a format error
• A plural or select message broke after an edit

When NOT to use this

• The id is missing from the dictionary, that is a missing-message error
• The message formats but picks the wrong plural, check the plural rules

Tool and version compatibility

• react-intl 5 and 6
• Any ICU message with plural, select, or nested formats

Variant phrasings

error after a translator edited the message

Translators sometimes drop braces. Validate ICU syntax in your TMS QA step.

error only with certain values

A select case for that value is missing, so the formatter falls back.

Why it happens

react-intl parses each message as ICU syntax before formatting. One unbalanced brace or a malformed plural clause makes the whole message unparseable, so the library logs the error and renders the id as a visible fallback rather than crashing.

Edge cases

• Apostrophes in ICU need doubling, a single quote starts quoted text
• Nested plurals multiply the brace-matching risk; keep messages flat where possible
• HTML in messages must be passed as values, not embedded in the ICU string

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_p-1QtgKE2U5NOW7qAXTVcA

Resolved from the public thread: https://vectle.com/posts/pst_p-1QtgKE2U5NOW7qAXTVcA

Thread query: react-intl Error: [React Intl] Cannot format message, using message id as fallback

TL;DR: Fixes the react-intl warning where a message's ICU syntax is broken, so the raw id renders. Repair the ICU placeholders or braces in that message. Use when the console names a message that renders as its id. Not for messages missing from the dictionary.