JSON.parse allows null as value

Question

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 come 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?

Answer 1

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.