JSON.parse parses JSON.stringify output but not string itself

Question

I just got this in the Chrome console:

JSON.stringify(({wat:"\""}))
> "{"wat":"\""}"
JSON.parse(JSON.stringify(({wat:"\""})))
> Object {wat: """}
JSON.parse('{"wat":"\""}')
> VM34235:1 Uncaught SyntaxError: Unexpected string in JSON at position 9(…)

Screenshot:

JSON.parse successfully parses when passed the output of JSON.stringify({wat:"\""}) but throws when I try to eval JSON.parse('{"wat":"\""}').

I'm calling shenanigans.

Look at the string value of '{"wat":"\""}'. It should be pretty clear then. — Felix Kling
– Felix Kling, Commented May 21, 2016 at 0:52
'{"wat":"\""}' === '{"wat":"""}'; // true, you need to escape your backslash — Paul S.
– Paul S., Commented May 21, 2016 at 0:57
If you look at the console output ("{"wat":"\""}"), you can see that the value is not a valid string literal, because it doesn't show escape sequences. Otherwise it would have to look like "{\"wat\":\"\\\"\"}". Hence you cannot simply copy and paste the output into a string literal. What the console shows you is the string value. This might become more obvious if you type 'foo\nbar' into the console. — Felix Kling
– Felix Kling, Commented May 21, 2016 at 1:00
Yeah, I should have figured that out. I was debugging some code which put a stringified object into a template string which was eval'd later, and tried to parse the same, confused me enough to forget about proper escaping... — Mosho
– Mosho, Commented May 21, 2016 at 1:03

Michał Perłakowski · Accepted Answer · 2016-05-21 00:53:40Z

5

The quote character has to be escaped with two backslashes, like that:

JSON.parse('{"wat":"\\""}')

When it's escaped with only one backslash, JSON.parse() actually gets the following value to parse:

{"wat":"""}

which is of course invalid JSON.

edited May 21, 2016 at 0:53

answered May 21, 2016 at 0:51

Michał Perłakowski

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1 Comment

andersfylling Over a year ago

Can't he just add more double qoutes as well? \"""

Hristijan Ilieski · Accepted Answer · 2016-05-21 00:56:56Z

0

Try adding 2 backslashes like this. JS sees the \ as an escape character and ignores it. So:

{wat:"\\""}

answered May 21, 2016 at 0:56

Hristijan Ilieski

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