@koa/is-json

Check if a body is JSON.

Install

npm install @koa/is-json

Usage

import { createReadStream } from 'node:fs'
import isJSON from '@koa/is-json'

isJSON({ message: 'hello' }) // true
isJSON([1, 2, 3]) // true
isJSON('hello') // false
isJSON(Buffer.from('hello')) // false
isJSON(createReadStream('file.txt')) // false
isJSON(null) // false
isJSON(1n) // true

CommonJS:

const { isJSON } = require('@koa/is-json')

API

isJSON(body?)

isJSON returns true for truthy values, except strings, buffers, and values with a callable pipe property. It returns false otherwise.

Types

Use JsonValue for JSON data: strings, numbers, booleans, null, and arrays or objects containing those values.

Use Jsonifiable when your data also contains values with a toJSON method, such as Date objects.

Use JsonBody for a body that could be Jsonifiable, a buffer, a readable stream, or an object with a callable pipe method. A value with this type can still return false from isJSON.

import { Buffer } from 'node:buffer'
import type { JsonValue, Jsonifiable, JsonBody } from '@koa/is-json'

const value: JsonValue = { message: 'hello', count: 2 }
const serializable: Jsonifiable = { createdAt: new Date() }
const body: JsonBody = Buffer.from('hello')

The package also exports JsonPrimitive, JsonObject, and JsonArray for individual JSON shapes, and PipeableBody for objects with a callable pipe method.

Breaking changes

Moving from koa-is-json to @koa/is-json is low effort.

Replace koa-is-json with @koa/is-json in your dependencies.

koa-is-json assigns the function to module.exports where @koa/is-json ships named and default exports.

so just do this:

-const isJSON = require('koa-is-json')
+const { isJSON } = require('@koa/is-json')

ESM callers are unaffected: import isJSON from '@koa/is-json' still works.

License

MIT