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Метод JSON.stringify() перетворює значення JavaScript в рядок JSON, додатково замінюючи значення (необов'язково) якщо задана функція "replacer" або включаючи лише вказані властивості, якщо вказаний масив "replacer".


JSON.stringify(value[, replacer[, space]])


Значення яке перетвориться на рядок JSON.
replacer Optional
A function that alters the behavior of the stringification process, or an array of String and Number objects that serve as a whitelist for selecting the properties of the value object to be included in the JSON string. If this value is null or not provided, all properties of the object are included in the resulting JSON string.
space Optional
Значення типу String або Number що використовується для додавання пропусків у результат функції щоб покращити читабельність вихідного JSON. Якщо це число - воно вказує кількість пробілів в одному відступі. Якщо передати число більше за 10, буде використано 10.  Значення менші за 1 вказують на те що відступи не використовуватимуться. Якщо це рядок, то цей рядок (або його перші 10 символів, якщо він надто довгий) будуть використовуватись в якості відступу. Якщо параметр не задано (або null), то відступи не додаватимуться.

Return value

A JSON string representing the given value.


JSON.stringify() converts a value to JSON notation representing it:

  • Properties of non-array objects are not guaranteed to be stringified in any particular order. Do not rely on ordering of properties within the same object within the stringification.
  • Boolean, Number, and String objects are converted to the corresponding primitive values during stringification, in accord with the traditional conversion semantics.
  • If undefined, a function, or a symbol is encountered during conversion it is either omitted (when it is found in an object) or censored to null (when it is found in an array). JSON.stringify can also just return undefined when passing in "pure" values like JSON.stringify(function(){}) or JSON.stringify(undefined).
  • All symbol-keyed properties will be completely ignored, even when using the replacer function.
  • Non-enumerable properties will be ignored
JSON.stringify({});                  // '{}'
JSON.stringify(true);                // 'true'
JSON.stringify('foo');               // '"foo"'
JSON.stringify([1, 'false', false]); // '[1,"false",false]'
JSON.stringify({ x: 5 });            // '{"x":5}'

JSON.stringify(new Date(2006, 0, 2, 15, 4, 5)) 
// '"2006-01-02T15:04:05.000Z"'

JSON.stringify({ x: 5, y: 6 });
// '{"x":5,"y":6}' or '{"y":6,"x":5}'
JSON.stringify([new Number(1), new String('false'), new Boolean(false)]);
// '[1,"false",false]'

JSON.stringify({ x: [10, undefined, function(){}, Symbol('')] }); 
// '{"x":[10,null,null,null]}' 
// Symbols:
JSON.stringify({ x: undefined, y: Object, z: Symbol('') });
// '{}'
JSON.stringify({ [Symbol('foo')]: 'foo' });
// '{}'
JSON.stringify({ [Symbol.for('foo')]: 'foo' }, [Symbol.for('foo')]);
// '{}'
JSON.stringify({ [Symbol.for('foo')]: 'foo' }, function(k, v) {
  if (typeof k === 'symbol') {
    return 'a symbol';
// '{}'

// Non-enumerable properties:
JSON.stringify( Object.create(null, { x: { value: 'x', enumerable: false }, y: { value: 'y', enumerable: true } }) );
// '{"y":"y"}'

The replacer parameter

The replacer parameter can be either a function or an array. As a function, it takes two parameters, the key and the value being stringified. The object in which the key was found is provided as the replacer's this parameter. Initially it gets called with an empty key representing the object being stringified, and it then gets called for each property on the object or array being stringified. It should return the value that should be added to the JSON string, as follows:

  • If you return a Number, the string corresponding to that number is used as the value for the property when added to the JSON string.
  • If you return a String, that string is used as the property's value when adding it to the JSON string.
  • If you return a Boolean, "true" or "false" is used as the property's value, as appropriate, when adding it to the JSON string.
  • If you return any other object, the object is recursively stringified into the JSON string, calling the replacer function on each property, unless the object is a function, in which case nothing is added to the JSON string.
  • If you return undefined, the property is not included in the output JSON string.
Note: You cannot use the replacer function to remove values from an array. If you return undefined or a function then null is used instead.

Example with a function

function replacer(key, value) {
  if (typeof value === "string") {
    return undefined;
  return value;

var foo = {foundation: "Mozilla", model: "box", week: 45, transport: "car", month: 7};
var jsonString = JSON.stringify(foo, replacer);

The resulting JSON string is {"week":45,"month":7}.

Example with an array

If replacer is an array, the array's values indicate the names of the properties in the object that should be included in the resulting JSON string.

JSON.stringify(foo, ['week', 'month']);  
// '{"week":45,"month":7}', only keep "week" and "month" properties

The space argument

The space argument may be used to control spacing in the final string. If it is a number, successive levels in the stringification will each be indented by this many space characters (up to 10). If it is a string, successive levels will be indented by this string (or the first ten characters of it).

JSON.stringify({ a: 2 }, null, ' ');
// '{
//  "a": 2
// }'

Using a tab character mimics standard pretty-print appearance:

JSON.stringify({ uno: 1, dos: 2 }, null, '\t');
// returns the string:
// '{
//     "uno": 1,
//     "dos": 2
// }'

toJSON() behavior

If an object being stringified has a property named toJSON whose value is a function, then the toJSON() method customizes JSON stringification behavior: instead of the object being serialized, the value returned by the toJSON() method when called will be serialized. For example:

var obj = {
  foo: 'foo',
  toJSON: function() {
    return 'bar';
JSON.stringify(obj);        // '"bar"'
JSON.stringify({ x: obj }); // '{"x":"bar"}'

Issue with plain JSON.stringify for use as JavaScript

Note that JSON is not a completely strict subset of JavaScript, with two line terminators (Line separator and Paragraph separator) not needing to be escaped in JSON but needing to be escaped in JavaScript. Therefore, if the JSON is meant to be evaluated or directly utilized within JSONP, the following utility can be used:

function jsFriendlyJSONStringify (s) {
    return JSON.stringify(s).
        replace(/\u2028/g, '\\u2028').
        replace(/\u2029/g, '\\u2029');

var s = {
    a: String.fromCharCode(0x2028),
    b: String.fromCharCode(0x2029)
try {
    eval('(' + JSON.stringify(s) + ')');
} catch (e) {
    console.log(e); // "SyntaxError: unterminated string literal"

// No need for a catch
eval('(' + jsFriendlyJSONStringify(s) + ')');

// console.log in Firefox unescapes the Unicode if
//   logged to console, so we use alert
alert(jsFriendlyJSONStringify(s)); // {"a":"\u2028","b":"\u2029"}

Example of using JSON.stringify() with localStorage

In a case where you want to store an object created by your user and allowing it to be restored even after the browser has been closed, the following example is a model for the applicability of JSON.stringify():

Functions are not a valid JSON data type so they will not work. However, they can be displayed if first converted to a string (e.g. in the replacer), via the function's toString method. Also, some objects like Date will be a string after JSON.parse().

// Creating an example of JSON
var session = {
  'screens': [],
  'state': true
session.screens.push({ 'name': 'screenA', 'width': 450, 'height': 250 });
session.screens.push({ 'name': 'screenB', 'width': 650, 'height': 350 });
session.screens.push({ 'name': 'screenC', 'width': 750, 'height': 120 });
session.screens.push({ 'name': 'screenD', 'width': 250, 'height': 60 });
session.screens.push({ 'name': 'screenE', 'width': 390, 'height': 120 });
session.screens.push({ 'name': 'screenF', 'width': 1240, 'height': 650 });

// Converting the JSON string with JSON.stringify()
// then saving with localStorage in the name of session
localStorage.setItem('session', JSON.stringify(session));

// Example of how to transform the String generated through 
// JSON.stringify() and saved in localStorage in JSON object again
var restoredSession = JSON.parse(localStorage.getItem('session'));

// Now restoredSession variable contains the object that was saved
// in localStorage


Specification Status Comment
ECMAScript 5.1 (ECMA-262)
The definition of 'JSON.stringify' in that specification.
Standard Initial definition. Implemented in JavaScript 1.7.
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'JSON.stringify' in that specification.
ECMAScript Latest Draft (ECMA-262)
The definition of 'JSON.stringify' in that specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) 3.5 (1.9.1) 8.0 10.5 4.0
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) 1.0 (1.0) (Yes) (Yes) (Yes)

See also

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 Зробили внесок у цю сторінку: linevich, tbunyk
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