为什么我会收到意外令牌\\

Question

k ="[{\"id\": 1, \"latitude\": \"52.511467\", \"longitude\": \"13.447179\", \"bearing\": \"0.000000\", \"speed\": \"0.000000\", \"device_status\": 0, \"timestamp\": \"2013-08-18 00:00:00\"}, {\"id\": 3, \"latitude\": \"53.511467\", \"longitude\": \"14.447179\", \"bearing\": \"1.000000\", \"speed\": \"1.000000\", \"device_status\": 2, \"timestamp\": \"2013-08-18 00:00:00\"}, {\"id\": 4, \"latitude\": \"54.511467\", \"longitude\": \"15.447179\", \"bearing\": \"1.000000\", \"speed\": \"1.000000\", \"device_status\": 2, \"timestamp\": \"2013-08-18 00:00:00\"}, {\"id\": 5, \"latitude\": \"33.511467\", \"longitude\": \"72.447179\", \"bearing\": \"1.000000\", \"speed\": \"1.000000\", \"device_status\": 1, \"timestamp\": \"2013-08-18 00:00:00\"}]"

R = JSON.parse(k)

SyntaxError: Unexpected token \\

whereas

m =JSON.parse("[{\"id\": 2, \"da\": \"1\"}]")

is working without error

Answer 1

It's because when it get's returned from the server, the result is getting store as a string, so the string itself contains the \\ escape character before every " . It isint valid to escape the " character in a JSON string.

It's like doing:

var json = '{\\"test\\":\\"test\\"}';
json //"{\"test\":\"test\"}"
JSON.parse(json); //SyntaxError: Unexpected token \

However, when you take that string and put it directly in the console, the \\ characters will play their escape role and will not be part of the actual string at the end. Basically, the JSON string produced server-side should not escape the " characters.

You could also replace the invalid ecape sequences client-side, but I would not recommend this:

JSON.parse(json.replace(/\\"/g, '"'));

Answer 2

Based on your image from the comments, you didn't tell the whole story in your post. If you do a console.log(k), you will notice it looks nothing like what you see in your console as output by currentTrackData:

>>> [{\"id\": 1, \"latitude\": \"52.511467\", \"longitude\": \"13.447179\", \"bearing\": \"0.000000\", \"speed\": \"0.000000\", \"device_status\": 0, \"timestamp\": \"2013-08-18 00:00:00\"}, {\"id\": 3, \"latitude\": \"53.511467\", \"longitude\": \"14.447179\", \"bearing\": \"1.000000\", \"speed\": \"1.000000\", \"device_status\": 2, \"timestamp\": \"2013-08-18 00:00:00\"}, {\"id\": 4, \"latitude\": \"54.511467\", \"longitude\": \"15.447179\", \"bearing\": \"1.000000\", \"speed\": \"1.000000\", \"device_status\": 2, \"timestamp\": \"2013-08-18 00:00:00\"}, {\"id\": 5, \"latitude\": \"33.511467\", \"longitude\": \"72.447179\", \"bearing\": \"1.000000\", \"speed\": \"1.000000\", \"device_status\": 1, \"timestamp\": \"2013-08-18 00:00:00\"}]

tells us that the string contains \\" . If you assign that thing to a var,

var k = "[{...\"..}]"
console.log(k);
>>> [{..."...}]

then you're explicitly solving the problem because those \\" are turned into " in your string. If you pass the output straight into JSON.parse, then there are a million slashes in the input, making it illegal JSON.

If this is server-generated, fix the generator. It shouldn't be escaping that string for you. If you don't have that luxury, then do a string replacement.

var u = currentTrackData...;
u = u.replace(/\\"/g, '"');
JSON.parse(u);