JSON6 Error Messages

Every JSON6 parse failure is a plain JavaScript Error. It is not a SyntaxError, so err instanceof SyntaxError is false, and it has no line or column property. The position is only in the message text. Match on the message, not the class, and read the line and column from the trailing [line:col].

Most messages share one shape. Here is a real one, produced by a missing comma:

The parser reports the first character it cannot accept, which is often one token after the real mistake. For a missing comma, the error points at the start of the next key. Always look at the character before the position too.

These mean the punctuation between members is wrong: a missing or doubled comma, a stray bracket, a key with no value.

fault parsing '<char>' unexpected

Triggered by:

Cause. The catch-all. The parser met a character that cannot start or continue anything at that point. By far the most common cause is a missing comma between two members, which makes the next key look like a stray word. Bare words that are not keywords ({a:b}), a : inside an array, and characters such as @ or # land here too.

Fix. Look at the character in brackets inside near and the one just before it. Add the missing comma, quote the value if it is a string, or delete the stray character.

Two values with no separator between them

Triggered by:

Cause. Two literals appeared in a row with only whitespace between them: numbers, or true, false, null.

Fix. Insert the comma. Note that [1 /* c */ 2] fails the same way, because a comment is not a separator.

String unexpected

Triggered by:

Cause. A string started where a value was already complete, again usually a missing comma.

Fix. Add the comma before the string.

String begin after previous value

Triggered by:

Cause. Inside an object, two key strings appeared back to back, so the first key never got its : and value.

Fix. Complete the first member ("a": 1,) or remove the extra key.

bad context; excessive commas while parsing;

Triggered by:

Cause. A comma in a place that has no empty slot. Arrays tolerate doubled commas (they create empty members), but objects do not, and a comma at the very top level is meaningless. A comma straight after a bare key ({a,}) also lands here.

Fix. Delete the extra comma. In an array, remember that [1,,2] is legal and has three slots, with the middle one empty.

Unexpected comma after object field name

Triggered by:

Cause. A key and its colon are present, but the value is missing and a comma follows.

Fix. Supply the value, or delete the whole member.

Object field name with no value

Triggered by:

Cause. A key was followed by } with no colon and value. This is the error you get when you try to write a set, or forget the :.

Fix. Write key: value. JSON6 has no shorthand like JavaScript's { a }.

Fault while parsing field value, close with no value

Triggered by:

Cause. A colon was followed directly by the closing brace.

Fix. Put a value after the colon (null or undefined if you really mean nothing).

Fault while parsing; unexpected

Triggered by:

Cause. A closing } showed up where the innermost open container is an array (or where nothing is open at all). The word "unexpected" appears twice in the full message because the generic suffix is appended to a leader that already says it.

Fix. Make the closer match its opener: [ closes with ], { with }. Indent the file consistently and the mismatch jumps out.

bad context N; fault while parsing

Triggered by:

Cause. The mirror of the previous error: a ] where an object (or nothing) is open. The number after "bad context" is an internal parser state code (0 means top level), not a line number. Ignore it and read the position at the end of the message.

Fix. Match the brackets, as above.

Unexpected array open after previous value

Triggered by:

Cause. A [ started right after a finished value inside an object.

Fix. Add the comma, or give the array its own key.

fault while parsing; getting field name unexpected

Triggered by:

Cause. An object or array was used where a key belongs. Keys must be a bare word, a number, or a quoted string. The two messages differ only in capitalization and wording: { gives the lowercase form, [ gives "Fault while parsing; while getting field name unexpected".

Fix. Use a string key. If you wanted nesting, put the container on the value side of a colon.

fault while parsing; quote not at start of field name

Triggered by:

Cause. A quote character appeared in the middle of a bare key. Bare keys cannot contain quotes of any kind.

Fix. Quote the entire key: "a'b": 1.

fault while parsing; character unexpected

Triggered by:

Cause. Whitespace ended a bare key and another word began before the colon. Bare keys cannot contain spaces.

Fix. Quote the key ("a b": 1) or remove the space.

(outside any object, got colon out of string):parsing fault;

Triggered by:

Cause. A : turned up where no key is waiting for a value: after a finished value, at the top level, or after a quoted string that is the whole document. Also the symptom of pasting a fragment of an object ("a": 1) without its braces. (The message says "outside any object" even for the inside-an-array and after-a-value cases.)

Fix. Wrap the fragment in { }, or remove the extra colon.

fault while parsing; '<char>' unexpected

Triggered by:

Cause. A / must begin // or /*. Anything else after a slash is an error, which also means JSON6 has no regular expression or division syntax. (A slash followed by a space reports the space as the offending character.)

Fix. Remove the slash, or quote the value if it is a path: "/x".

Escapes are validated while the string is being read, so the position points inside the string.

Incomplete hexidecimal sequence

Triggered by:

Cause. A \x escape needs exactly two hex digits and the string closed after one. (The word is spelled "hexidecimal" in the library's message; search for it that way.)

Fix. Write \x01.

Incomplete unicode sequence

Triggered by:

Cause. A \u escape needs exactly four hex digits.

Fix. Pad to four digits (\u0012) or use the braced form (\u{12}).

Incomplete long unicode sequence

Triggered by:

Cause. A \u{ escape was never closed with }.

Fix. Close the brace.

(escaped character, parsing hex of \u) or (... of \x)

Triggered by:

Cause. A non-hex character appeared inside an escape.

Fix. Use only 0-9, a-f, A-F. If you meant a literal backslash, double it: \\.

RangeError: Invalid code point

Triggered by:

Cause. The braced escape named a code point above U+10FFFF. This is the one parse error that is a RangeError and carries no position, because it is thrown by String.fromCodePoint rather than by the parser.

Fix. Use a code point up to 10FFFF.

The streaming parser (JSON6.begin) shares every parse error above and adds the following. stringify() has exactly one error of its own.

context stack is not empty at flush

Cause. The streaming parser was flushed with write('') while a number was still being read inside an open object or array, as in {a:1. This is the only flush case that throws. If the cut-off comes after a string, a keyword or a closed inner container ({a:true), the flush succeeds silently and the unfinished value is simply never delivered, and an unterminated string is only reported if you call parser.finalError().

Fix. Check that the producer sent the closing bracket, or only flush at a real end of input. To validate a whole document, use JSON6.parse rather than relying on the flush.

Parser is in an error state, please reset.

Cause. After write() throws, the parser refuses further input until you call reset().

Fix. Catch the first error, log it, and call parser.reset() (or build a new parser) before writing again.

Callback function must be passed to begin, or you can't get values from the stream.

Cause. JSON6.begin() was called without a callback and then write() was used. begin() itself does not throw; the error appears on the first write().

Fix. Pass the callback: JSON6.begin((value) => { ... }).

JSON6.stringify unknown replacer type.

Cause. The second argument to stringify() was neither a function nor an array (for example a string or an options object).

Fix. Pass null for the replacer and use the fourth argument for options: JSON6.stringify(v, null, 2, { sortKeys: false }).