JSON.parse()

The JSON.parse() method parses a string as JSON, optionally transforming the value produced by parsing.

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, prescribes how the value originally produced by parsing is transformed, before being returned.

Returns

Returns the Object corresponding to the given JSON text.

Throws

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, which 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, e.g. 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.

The reviver is ultimately called with the empty string and the topmost value to permit transformation of the topmost value. Be certain to handle this case properly, usually by returning the provided value, or JSON.parse() will return undefined.

JSON.parse('{"p": 5}', function(k, v) {
  if (k === '') { return v; } // if topmost value, return it,
  return v * 2;               // else return v * 2.
});                           // { p: 10 }

JSON.parse('{"1": 1, "2": 2, "3": {"4": 4, "5": {"6": 6}}}', function(k, v) {
  console.log(k); // log the current property name, the last is "".
  return v;       // 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 10 of the JSON data

See also

• JSON.stringify()