JSON.parse()

The JSON.parse() method parses a JSON string, constructing the JavaScript value or object described by the string. An optional reviver function can be provided to perform a transformation on the resulting object before it is returned.

Syntax

JSON.parse(text[, reviver])

Parameters

text

The string to parse as JSON. See the JSON object for a description of JSON syntax.

reviver Optional

If a function, this prescribes how the value originally produced by parsing is transformed, before being returned.

Return value

The Object corresponding to the given JSON text.

Exceptions

Throws a SyntaxError exception if the string to parse is not valid JSON.

Examples

Using JSON.parse()

JSON.parse('{}');              // {}
JSON.parse('true');            // true
JSON.parse('"foo"');           // "foo"
JSON.parse('[1, 5, "false"]'); // [1, 5, "false"]
JSON.parse('null');            // null

Using the reviver parameter

If a reviver is specified, the value computed by parsing is transformed before being returned. Specifically, the computed value and all its properties (beginning with the most nested properties and proceeding to the original value itself) are individually run through the reviver. Then it is called, with the object containing the property being processed as this, and with the property name as a string, and the property value as arguments. If the reviver function returns undefined (or returns no value, for example, if execution falls off the end of the function), the property is deleted from the object. Otherwise, the property is redefined to be the return value.

If the reviver only transforms some values and not others, be certain to return all untransformed values as-is, otherwise they will be deleted from the resulting object.

JSON.parse('{"p": 5}', (key, value) =>
  typeof value === 'number'
    ? value * 2 // return value * 2 for numbers
    : value     // return everything else unchanged
);
// { p: 10 }
JSON.parse('{"1": 1, "2": 2, "3": {"4": 4, "5": {"6": 6}}}', (key, value) => {
  console.log(key); // log the current property name, the last is "".
  return value;     // return the unchanged property value.
});
// 1
// 2
// 4
// 6
// 5
// 3 
// ""

JSON.parse() does not allow trailing commas

// both will throw a SyntaxError
JSON.parse('[1, 2, 3, 4, ]');
JSON.parse('{"foo" : 1, }');

Specifications

Browser compatibility

Gecko-specific notes

Starting Gecko 29 (Firefox 29 / Thunderbird 29 / SeaMonkey 2.26), a malformed JSON string yields a more detailed error message containing the line and column number that caused the parsing error. This is useful when debugging large JSON data.

JSON.parse('[1, 2, 3, 4,]');
// SyntaxError: JSON.parse: unexpected character at
// line 1 column 13 of the JSON data

See also

• JSON.stringify()