JSON.stringify()

Baseline Widely available

This feature is well established and works across many devices and browser versions. Its been available across browsers since 2015 7.

Learn more
See full compatibility

JSON.stringify() JavaScript JSON . , replacer , .

console.log(JSON.stringify({ x: 5, y: 6 }));
// Expected output: '{"x":5,"y":6}'

console.log(
  JSON.stringify([new Number(3), new String("false"), new Boolean(false)]),
);
// Expected output: '[3,"false",false]'

console.log(JSON.stringify({ x: [10, undefined, function () {}, Symbol("")] }));
// Expected output: '{"x":[10,null,null,null]}'

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

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

value: JSON .
replacer Optional: , JSON (whitelist) String Number . null , JSON .
space Optional: JSON String Number . Number , (space) ; 10 10 . 1 . String , ( 10 , 10 ) . ( null ), .

JSON .

TypeError(cyclic object value).

JSON.stringify() JSON .

. .
Boolean, Number, String (primitive) .
undefined, , (symbol) ( ) null ( ).
replacer .
.

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]'

// 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"}'

`replacer`

replacer . key value, 2 . key this . key , . JSON :

Number , JSON .
String , JSON .
Boolean , JSON "true" "false" .
, replacer JSON . JSON .
undefined , JSON .

: : replacer . undefined null .

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);

JSON {"week":45,"month":7} .

replacer , JSON .

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

`space`

space . 10 , 10 .

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

'\t' .

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

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"}'

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
console.log(restoredSession);

Specification
ECMAScript 2027 LanguageSpecification # sec-json.stringify

JSON.parse()

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JSON

JSON.stringify()

In this article

`replacer`

`space`

`toJSON()`

Example of using `JSON.stringify()` with `localStorage`

Help improve MDN

JSON.stringify()

In this article

replacer

space

toJSON()

Example of using JSON.stringify() with localStorage

Help improve MDN

`replacer`

`space`

`toJSON()`

Example of using `JSON.stringify()` with `localStorage`