I am passing null to JSON.parse() and although the first parameter is documented saying that it should be a string value, it still works to supply null.

How e this does not throw an error even though even though the documentation state this is for strings and can this be safely and reliable used in multiple browsers?

I am passing null to JSON.parse() and although the first parameter is documented saying that it should be a string value, it still works to supply null.

How e this does not throw an error even though even though the documentation state this is for strings and can this be safely and reliable used in multiple browsers?

• javascript
• json

• check the below answer stackoverflow./questions/21120999/representing-null-in-json – Suvethan Nantha Commented Sep 28, 2017 at 8:32
• I feel like that question is different since it talks about using null within JSON objects. JSON objects that JSON.stringify has gone over resulting in strings. I simply throw null into my JSON.parse() directly. – Stephan-v Commented Sep 28, 2017 at 8:34
• I assume parse might internally cast the given value to a string, which would be "null", which is a valid JSON value. – deceze ♦ Commented Sep 28, 2017 at 8:34
• Ok if that is the case I wonder how reliable this is cross-browser. – Stephan-v Commented Sep 28, 2017 at 8:36
• JSON.parse("null") or JSON.parse(null) both of them are casted as "null" which is a valid json, but if you pass JSON.parse('') it will throw an exception it's an empty string – Suvethan Nantha Commented Sep 28, 2017 at 8:42

2 Answers 2

The ECMAScript spec says as the first step for JSON.parse:

1. Let JText be ToString(text).

Meaning it'll cast whatever argument it's given to a string, and null casts to "null", which is the valid JSON representation of null.

Note that a single such JSON primitive shouldn't be valid, a JSON string should be wrapped in an object or array. But parsers have traditionally been lax with that, partially due to it making the implementation simpler I suppose.

See the specification:

1. Let JText be ToString(text).

It doesn't require that the first argument be a string, it attempts to convert it to a string.

"" + null will give you "null" which is a string containing valid JSON.

This is also in the spec:

Null: Return "null".