JSON5 - BunDocumentation Index
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Skip to main contentBun home pageUse Bun’s built-in support for JSON5 files through both runtime APIs and bundler integration
import { JSON5 } from "bun";
const data = JSON5.parse(`{
// JSON5 supports comments
name: 'my-app',
version: '1.0.0',
debug: true,
// trailing commas are allowed
tags: ['web', 'api',],
}`);
console.log(data);
// {
// name: "my-app",
// version: "1.0.0",
// debug: true,
// tags: ["web", "api"]
// }
Supported JSON5 Features
JSON5 is a superset of JSON based on ECMAScript 5.1 syntax. It supports:
Comments: single-line (http://) and multi-line (/* */)
Trailing commas: in objects and arrays
Unquoted keys: valid ECMAScript 5.1 identifiers can be used as keys
Single-quoted strings: in addition to double-quoted strings
Multi-line strings: using backslash line continuations
Hex numbers: 0xFF
Leading & trailing decimal points: .5 and 5.
Infinity and NaN: positive and negative
Explicit plus sign: +42
const data = JSON5.parse(`{
// Unquoted keys
unquoted: 'keys work',
// Single and double quotes
single: 'single-quoted',
double: "double-quoted",
// Trailing commas
trailing: 'comma',
// Special numbers
hex: 0xDEADbeef,
half: .5,
to: Infinity,
nan: NaN,
// Multi-line strings
multiline: 'line 1 \
line 2',
}`);
Error Handling
Bun.JSON5.parse() throws a SyntaxError if the input is invalid JSON5:
try {
JSON5.parse("{invalid}");
} catch (error) {
console.error("Failed to parse JSON5:", error.message);
}
Bun.JSON5.stringify()
Stringify a JavaScript value to a JSON5 string.
import { JSON5 } from "bun";
const str = JSON5.stringify({ name: "my-app", version: "1.0.0" });
console.log(str);
// {name:'my-app',version:'1.0.0'}
Pretty Printing
Pass a space argument to format the output with indentation:
const pretty = JSON5.stringify(
{
name: "my-app",
debug: true,
tags: ["web", "api"],
},
null,
2,
);
console.log(pretty);
// {
// name: 'my-app',
// debug: true,
// tags: [
// 'web',
// 'api',
// ],
// }
The space argument can be a number (number of spaces) or a string (used as the indent character):
// Tab indentation JSON5.stringify(data, null, "\t");Special Values Unlike JSON.stringify, JSON5.stringify preserves special numeric values:
JSON5.stringify({ inf: Infinity, ninf: -Infinity, nan: NaN });
// {inf:Infinity,ninf:-Infinity,nan:NaN}
Module Import
ES Modules
You can import JSON5 files directly as ES modules:
config.json5{
// Database configuration
database: {
host: "localhost",
port: 5432,
name: "myapp",
},
features: {
auth: true,
rateLimit: true,
analytics: false,
},
}
Default Import
app.tsimport config from "./config.json5"; console.log(config.database.host); // "localhost" console.log(config.features.auth); // trueNamed Imports You can destructure top-level properties as named imports: app.ts
import { database, features } from "./config.json5";
console.log(database.host); // "localhost"
console.log(features.rateLimit); // true
CommonJS
JSON5 files can also be required in CommonJS:
app.tsconst config = require("./config.json5");
console.log(config.database.name); // "myapp"
// Destructuring also works
const { database, features } = require("./config.json5");
Hot Reloading with JSON5
When you run your application with bun --hot, changes to JSON5 files are automatically detected and reloaded:
config.json5{
server: {
port: 3000,
host: "localhost",
},
features: {
debug: true,
verbose: false,
},
}
server.tsimport { server, features } from "./config.json5";
Bun.serve({
port: server.port,
hostname: server.host,
fetch(req) {
if (features.verbose) {
console.log(`${req.method} ${req.url}`);
}
return new Response("Hello World");
},
});
Run with hot reloading:
terminalbun --hot server.tsBundler Integration When you import JSON5 files and bundle with Bun, the JSON5 is parsed at build time and included as a JavaScript module: terminal
bun build app.ts --outdir=distThis means: Zero runtime JSON5 parsing overhead in production Smaller bundle sizes Tree-shaking support for unused properties (named imports) Dynamic Imports JSON5 files can be dynamically imported:
const { default: config } = await import("./config.json5");
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