JJPWRGEM

JJPWRGEM JSON Parser With Really Good Error Messages

An RFC 8259 compliant JSON Parser and formatter!

$ echo -en "{\"coolKey\"}" | jjp check
error: expected colon after key, found `}`
 --> stdin:1:11
  |
1 | {"coolKey"}
  |  ---------^
  |  |
  |  expected due to `"coolKey"`
  |
help: insert colon and placeholder value
  |
1 | {"coolKey": "🐟🛹"}
  |           ++++++++

Table of contents

• Table of contents
• Installation
• Stability
• FAQ
• Motivations

Installation

Precompiled

mise use -g github:20jasper/jjpwrgem

See releases for shell and powershell installation instructions and raw binaries

Note: node adds ~60ms of overhead

npm install -g jjpwrgem

From source

cargo install --path .

Stability

JJPWRGEM is in its infancy and extremely likely to have breaking changes (properly marked with semver of course!)

Indeterminate Handling

How cases undefined by the spec are handled

• numbers of any size or length are allowed
  • the original precision will be maintained
  • -0 is not equal to 0 and will persist
• the last duplicate key is stored
  • escaped and unescaped characters are considered not equal
• parsing will fail if BOM is included
• only utf8 encoding is supported
• no limitations on nesting or length
• extensions such as trailing commas or comments are not allowed
• surrogates are not validated, eg a lone continuation byte is valid

Is it blazingly fast™?

Axolotls can't walk so fast, so skateboards are pretty fast 🛹🐟

jjpwrgem can parse and pretty print a 1.7MB JSON file in around ~11ms and the average package.json in ~500 microseconds

See the benchmarks for more info!

FAQ

What does JJPWRGEM stand for?

JJPWRGEM JSON Parser With Really Good Error Messages. I was inspired by GNU to make a recursive acronym

How do you pronounce JJPWRGEM?

/ˈdʒeɪ dʒeɪ ˈpaʊər dʒɛm/ JAY-jay-POW-er-jem

But why is it called that?

It sounds cool and the name isn't taken on any package managers

Why is the logo an axolotl riding a skateboard?

It's cool

How long is an axolotl?

According to the San Diego zoo, "[a]n axolotl can reach 12 inches in length, but on average grows to about 9 inches¹"

Motivations

I originally started this project to practice finite state machines, but got back into it when hearing about the internals of some formatters and compilers!

I am heavily inspired by the Rust compiler's error messages. I love that unhelpful errors are considered bugs

I checked out several JSON parsers and formatters, and none provided much context on why a key was missing. Errors ranged from "expected closing on byte 10" to a snapshot of source code for that character, but none were up to my standards

Footnotes

1. https://animals.sandiegozoo.org/animals/axolotl ↩