Parse JSON with special 'undefined' value?

问题

In addition to strings and numbers, valid JSON can contain special values null and false

I need to parse JSON that also contains undefined, which is a valid javascript value, but not a valid JSON value

Example

library(jsonlite)

# A string works
"[{\"Sepal.Width\":\"3.5\"}]" %>% fromJSON
#  Sepal.Width
#         3.5

# A number works
"[{\"Sepal.Width\":3.5}]"  %>% fromJSON
#  Sepal.Width
#         3.5

# null works
"[{\"Sepal.Width\": null}]" %>% fromJSON
#  Sepal.Width
#          NA

# false works
 "[{\"Sepal.Width\": false}]" %>% fromJSON
#  Sepal.Width
#       FALSE

# undefined does not work
 "[{\"Sepal.Width\": undefined}]" %>% fromJSON
Error: lexical error: invalid char in json text.
                      [{"Sepal.Width": undefined}]
                     (right here) ------^

Question

Is there any (reliable) way to parse JSON containing undefined?

Note

I've thought about simply gsubbing undefined, but that is risky, since that word could easily exist in the JSON string values.

回答1:

You cannot parse a JSON with an undefined value; undefined is special. In fact, undefined as a "value" must not occur in valid JSON.

The official source, The JSON Data Interchange Syntax, states that

A JSON value can be an object, array, number, string, true, false, or null.

The best remedy is to examine the JSON generator and why it generates undefined in a JSON.

来源：https://stackoverflow.com/questions/59304404/parse-json-with-special-undefined-value