Truncate a JSON string.

Examples

import truncateJson from 'truncate-json'

// Object properties and array items beyond `maxSize` are omitted.
const maxSize = 15
const jsonString = JSON.stringify({ a: 'one', b: 'two' })
console.log(jsonString)
// '{"a":"one","b":"two"}' (21 bytes)
console.log(truncateJson(jsonString, maxSize).jsonString)
// '{"a":"one"}' (11 bytes)

// Works deeply inside objects and arrays
const jsonString = JSON.stringify([
  'one',
  { a: 'two', b: { c: 'three', d: 'four' } },
  'five',
])
console.log(jsonString)
// '["one",{"a":"two","b":{"c":"three","d":"four"}},"five"]' (55 bytes)
const returnValue = truncateJson(jsonString, 40)
console.log(returnValue.jsonString)
// '["one",{"a":"two","b":{"c":"three"}}]' (37 bytes)

// Omitted/truncated properties are returned
console.log(returnValue.truncatedProps)
// [
//   { path: [ 1, 'b', 'd' ], value: 'four' },
//   { path: [ 2 ], value: 'five' }
// ]
const isTruncated = returnValue.truncatedProps.length !== 0
console.log(isTruncated) // true

// Indentation is automatically detected and preserved
const jsonString = JSON.stringify({ a: 'one', b: 'two' }, undefined, 2)
console.log(jsonString)
// '{
//   "a": "one",
//   "b": "two"
// }' (30 bytes)
console.log(truncateJson(jsonString, 25).jsonString)
// '{
//   "a": "one"
// }' (16 bytes)

// The top-level value can be any JSON type, not only objects or arrays
const jsonString = JSON.stringify('This is an example top-level string')
console.log(truncateJson(jsonString, 25).jsonString)
// '"This is an example t..."' (25 bytes)

Install

npm install truncate-json

This package works in both Node.js >=18.18.0 and browsers.

This is an ES module. It must be loaded using an import or import() statement, not require(). If TypeScript is used, it must be configured to output ES modules, not CommonJS.

API

truncateJson(jsonString, maxSize)

jsonString string
maxSize number
Return value: object

Truncates a JSON string to maxSize bytes.

Any object property or array item beyond the maxSize limit is completely omitted. Strings are not truncated, except when at the top-level.

Return value

The return value is an object with the following properties.

jsonString

Type: string

jsonString after truncation has been applied.

truncatedProps

Type: object[]

List of properties having been truncated/omitted.

truncatedProps[*].path

Type: Array<string | number>

Property path. This is an array of property keys and/or array indices.

truncatedProps[*].value

Type: JsonValue

Property value.

Related projects

• is-json-value: Check if a value is valid JSON
• safe-json-value: ⛑️ JSON serialization should never fail
• guess-json-indent: Guess the indentation of a JSON string
• string-byte-length: Get the UTF-8 byte length of a string
• string-byte-slice: Like string.slice() but bytewise

Support

For any question, don't hesitate to submit an issue on GitHub.

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