As of jQuery 3.0, $.parseJSON is deprecated. To parse JSON strings use the native JSON.parse method instead.

Passing in a malformed JSON string results in a JavaScript exception being thrown. For example, the following are all invalid JSON strings:

• "{test: 1}" (test does not have double quotes around it).
• "{'test': 1}" ('test' is using single quotes instead of double quotes).
• "'test'" ('test' is using single quotes instead of double quotes).
• ".1" (a number must start with a digit; "0.1" would be valid).
• "undefined" (undefined cannot be represented in a JSON string; null, however, can be).
• "NaN" (NaN cannot be represented in a JSON string; direct representation of Infinity is also not permitted).

The JSON standard does not permit "control characters" such as a tab or newline. An example like $.parseJSON( '{ "testing":"1\t2\n3" }' ) will throw an error in most implementations because the JavaScript parser converts the string's tab and newline escapes into literal tab and newline; doubling the backslashes like "1\\t2\\n3" yields expected results. This problem is often seen when injecting JSON into a JavaScript file from a server-side language such as PHP.

Where the browser provides a native implementation of JSON.parse, jQuery uses it to parse the string. For details on the JSON format, see https://json.org/.

Prior to jQuery 1.9, $.parseJSON returned null instead of throwing an error if it was passed an empty string, null, or undefined, even though those are not valid JSON.