Parsing JSONC

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JSONC is JSON extended with comments and trailing commas, which makes it a friendlier format for configuration files that humans edit. Deno reads its own deno.jsonc config file in this format. The Standard Library provides a parser for it in jsr:@std/jsonc.

import { parse } from "jsr:@std/jsonc";

This config uses line comments, a block comment and trailing commas. All three are valid JSONC.

const text = `{

The name appears in log output.

  "name": "my-app",
  /* Ports below 1024 need extra privileges. */
  "port": 8080,
  "features": [
    "http",
    "websockets",
  ],
}`;

To parse, pass the text to the parse function. Comments and trailing commas are dropped and a plain JavaScript value comes back.

const config = parse(text);
console.log(config); // { name: "my-app", port: 8080, features: [ "http", "websockets" ] }

The return type is JsonValue, so cast it to the shape you expect before accessing properties.

const { name, port } = config as { name: string; port: number };
console.log(name, port); // my-app 8080

The built-in JSON.parse rejects the same text, because comments and trailing commas are not valid JSON. It throws on the first comment.

try {
  JSON.parse(text);
} catch (error) {
  console.log((error as Error).name); // SyntaxError
}

Run this example locally using the Deno CLI:

deno run https://docs.deno.com/examples/scripts/parsing_jsonc.ts

Parsing JSONC

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