⛑️ JSON serialization should never fail.

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Features

Prevent JSON.stringify() from:

• Throwing
• Changing types
• Filtering or transforming values unexpectedly

Example

import safeJsonValue from 'safe-json-value'

const input = { one: true }
input.self = input

JSON.stringify(input) // Throws due to cycle
const { value, changes } = safeJsonValue(input)
JSON.stringify(value) // '{"one":true}"

console.log(changes) // List of changed properties
// [
//   {
//     path: ['self'],
//     oldValue: <ref *1> { one: true, self: [Circular *1] },
//     newValue: undefined,
//     reason: 'unsafeCycle'
//   }
// ]

Install

npm install safe-json-value

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

safeJsonValue(value, options?)

value any
options Options?
Return value: object

Makes value JSON-safe by:

• Omitting properties which would throw, change type unexpectedly or be filtered with JSON.stringify()
• Resolving properties which would change value with JSON.stringify()

This never throws.

Options

Object with the following properties.

maxSize

Type: number
Default: 1e7

Big JSON strings can make a process, filesystem operation or network request crash. maxSize prevents it by setting a maximum JSON.stringify(value).length.

Additional properties beyond the size limit are omitted. They are completely removed, not truncated (including strings).

const input = { one: true, two: 'a'.repeat(1e6) }
JSON.stringify(safeJsonValue(input, { maxSize: 1e5 }).value) // '{"one":true}"

shallow

Type: boolean
Default: false

If false, object/array properties are processed recursively. Please note that cycles are not removed when this is true.

Return value

Object with the following properties.

value

Type: any

Copy of the input value after applying all the changes to make it JSON-safe.

The top-level value itself might be changed (including to undefined) if it is either invalid JSON or has a toJSON() method.

The value is not serialized to a JSON string. This allows choosing the serialization format (JSON, YAML, etc.), processing the value, etc.

changes

Type: Change[]

List of changes applied to value. Each item is an individual change to a specific property. A given property might have multiple changes, listed in order.

changes[*].path

Type: Array<string | symbol | number>

Property path.

changes[*].oldValue

Type: any

Property value before the change.

changes[*].newValue

Type: any

Property value after the change. undefined means the property was omitted.

changes[*].reason

Type: string

Reason for the change among:

• Exceptions: "unsafeCycle", "unsafeBigInt", "unsafeSize", "unsafeException", "unsafeToJSON", "unsafeGetter"
• Invalid descriptors: "descriptorNotWritable", "descriptorNotConfigurable"
• Unexpected types: "unstableInfinite"
• Filtered values: "ignoredFunction", "ignoredUndefined", "ignoredSymbolValue", "ignoredSymbolKey", "ignoredNotEnumerable", "ignoredArrayProperty"
• Unresolved values: "unresolvedToJSON", "unresolvedClass", "unresolvedGetter"

changes[*].error

Type: Error?

Error that triggered the change. Only present if reason is "unsafeException", "unsafeToJSON" or "unsafeGetter".

Changes

This is a list of all possible changes applied to make the value JSON-safe.

Exceptions

JSON.stringify() can throw on specific properties. Those are omitted.

Cycles

const input = { one: true }
input.self = input
JSON.stringify(input) // Throws due to cycle
JSON.stringify(safeJsonValue(input).value) // '{"one":true}"

Infinite recursion

const input = { toJSON: () => ({ one: true, input }) }
JSON.stringify(input) // Throws due to infinite `toJSON()` recursion
JSON.stringify(safeJsonValue(input).value) // '{"one":true,"input":{...}}"

BigInt

const input = { one: true, two: 0n }
JSON.stringify(input) // Throws due to BigInt
JSON.stringify(safeJsonValue(input).value) // '{"one":true}"

Big output

const input = { one: true, two: '\n'.repeat(5e8) }
JSON.stringify(input) // Throws due to max string length
JSON.stringify(safeJsonValue(input).value) // '{"one":true}"

Exceptions in toJSON()

const input = {
  one: true,
  two: {
    toJSON: () => {
      throw new Error('example')
    },
  },
}
JSON.stringify(input) // Throws due to `toJSON()`
JSON.stringify(safeJsonValue(input).value) // '{"one":true}"

Exceptions in getters

const input = {
  one: true,
  get two() {
    throw new Error('example')
  },
}
JSON.stringify(input) // Throws due to `get two()`
JSON.stringify(safeJsonValue(input).value) // '{"one":true}"

Exceptions in proxies

const input = new Proxy(
  { one: false },
  {
    get: () => {
      throw new Error('example')
    },
  },
)
JSON.stringify(input) // Throws due to proxy
JSON.stringify(safeJsonValue(input).value) // '{}'

Invalid descriptors

Non-writable properties

const input = {}
Object.defineProperty(input, 'one', {
  value: true,
  enumerable: true,
  writable: false,
  configurable: true,
})
input.one = false // Throws: non-writable
const safeInput = safeJsonValue(input).value
safeInput.one = false // Does not throw: now writable

Non-configurable properties

const input = {}
Object.defineProperty(input, 'one', {
  value: true,
  enumerable: true,
  writable: true,
  configurable: false,
})
// Throws: non-configurable
Object.defineProperty(input, 'one', { value: false, enumerable: false })
const safeInput = safeJsonValue(input).value
// Does not throw: now configurable
Object.defineProperty(safeInput, 'one', { value: false, enumerable: false })

Unexpected types

JSON.stringify() changes the types of specific values unexpectedly. Those are omitted.

NaN and Infinity

const input = { one: true, two: Number.NaN, three: Number.POSITIVE_INFINITY }
JSON.stringify(input) // '{"one":true,"two":null,"three":null}"
JSON.stringify(safeJsonValue(input).value) // '{"one":true}"

Invalid array items

const input = [true, undefined, Symbol(), false]
JSON.stringify(input) // '[true, null, null, false]'
JSON.stringify(safeJsonValue(input).value) // '[true, false]'

Filtered values

JSON.stringify() omits some specific types. Those are omitted right away to prevent any unexpected output.

Functions

const input = { one: true, two: () => {} }
JSON.parse(JSON.stringify(input)) // { one: true }
safeJsonValue(input).value // { one: true }

undefined

const input = { one: true, two: undefined }
JSON.parse(JSON.stringify(input)) // { one: true }
safeJsonValue(input).value // { one: true }

Symbol values

const input = { one: true, two: Symbol() }
JSON.parse(JSON.stringify(input)) // { one: true }
safeJsonValue(input).value // { one: true }

Symbol keys

const input = { one: true, [Symbol()]: true }
JSON.parse(JSON.stringify(input)) // { one: true }
safeJsonValue(input).value // { one: true }

Non-enumerable keys

const input = { one: true }
Object.defineProperty(input, 'two', { value: true, enumerable: false })
JSON.parse(JSON.stringify(input)) // { one: true }
safeJsonValue(input).value // { one: true }

Array properties

const input = [true]
input.prop = true
JSON.parse(JSON.stringify(input)) // [true]
safeJsonValue(input).value // [true]

Unresolved values

JSON.stringify() can transform some values. Those are resolved right away to prevent any unexpected output.

toJSON()

const input = {
  toJSON: () => ({ one: true }),
}
JSON.parse(JSON.stringify(input)) // { one: true }
safeJsonValue(input).value // { one: true }

Dates

const input = { one: new Date() }
JSON.parse(JSON.stringify(input)) // { one: '2022-07-29T14:37:40.865Z' }
safeJsonValue(input).value // { one: '2022-07-29T14:37:40.865Z' }

Classes

const input = { one: new Set([]) }
JSON.parse(JSON.stringify(input)) // { one: {} }
safeJsonValue(input).value // { one: {} }

Getters

const input = {
  get one() {
    return true
  },
}
JSON.parse(JSON.stringify(input)) // { one: true }
safeJsonValue(input).value // { one: true }

Proxies

const input = new Proxy(
  { one: false },
  {
    get: () => true,
  },
)
JSON.parse(JSON.stringify(input)) // { one: true }
safeJsonValue(input).value // { one: true }

Related projects

• is-json-value: Check if a value is valid JSON
• truncate-json: Truncate a JSON string
• guess-json-indent: Guess the indentation of a JSON string
• error-serializer: Convert errors to/from plain objects

Support

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

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Contributing

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