src/stream/ndjson/transformToNDJson.ts
import { Transform } from 'node:stream'
import { _sortObjectDeep } from '@naturalcycles/js-lib'
import { TransformTyped } from '../stream.model'
export interface TransformToNDJsonOptions {
/**
* If true - will throw an error on JSON.parse / stringify error
*
* @default true
*/
strict?: boolean
/**
* If true - will run `sortObjectDeep()` on each object to achieve deterministic sort
*
* @default false
*/
sortObjects?: boolean
/**
* @default `\n`
*/
separator?: string
}
/**
* Transforms objects (objectMode=true) into chunks \n-terminated JSON strings (readableObjectMode=false).
*/
export function transformToNDJson<IN = any>(
opt: TransformToNDJsonOptions = {},
): TransformTyped<IN, string> {
const { strict = true, separator = '\n', sortObjects = false } = opt
return new Transform({
writableObjectMode: true,
readableObjectMode: false,
readableHighWaterMark: 64 * 1024,
transform(chunk: IN, _, cb) {
try {
if (sortObjects) {
chunk = _sortObjectDeep(chunk as any)
}
cb(null, JSON.stringify(chunk) + separator)
} catch (err) {
console.error(err)
if (strict) {
cb(err as Error) // emit error
} else {
cb() // emit no error, but no result neither
}
}
},
})
}