$.parseJSON(resp); if resp is number it works

Question

I was using this to test if server returned data is json.

try {
    json = $.parseJSON(resp);
} catch (error) {
    json = null;
}

if (json) {
    //
} else {
    //
}

But it returns true if resp is a number lik 2 or 3 or... It returns null if resp is 0.

Any ideas how to avoid this false situation?

I'm outputting data using php:

echo 0; //returns null
echo 2; //returns as valid json

It appears, 0 is read as string, and 2 is read as number.

I don't get `null` when I test it. And what is meant by "returns true"? Are you using the result as a condition? If so, `0` is falsey. More info is needed — cookie monster, Dec 23 '13 at 16:24
Do you want to know if `json` is an object ? If so use `typeof json==="object"`. — Denys Séguret, Dec 23 '13 at 16:24
`$.parseJSON('0');` works but `$.parseJSON(0);` returns null. — p.s.w.g, Dec 23 '13 at 16:25
@dystroy I'm trying to understand if response is valid json. — , Dec 23 '13 at 16:27
@cookiemonster Yes, that's my point. Strings work, numbers don't. — p.s.w.g, Dec 23 '13 at 16:30
@p.s.w.g: My point is that other numbers worked, so we're certainly dealing with strings. — cookie monster, Dec 23 '13 at 16:38
@cookiemonster Unless OP was comparing strings before and numbers now. As it stands now, the question doesn't present enough information to reproduce the issue. — p.s.w.g, Dec 23 '13 at 16:41
Can you inspect the actual HTTP response, e.g. in your browser's developer console or in fiddler? I suspect the real problem is how your sending the response from the server. — p.s.w.g, Dec 23 '13 at 16:46
What you're not showing is the manner in which you've tested the response that has caused you to determine that `json` is `null` — cookie monster, Dec 23 '13 at 16:47
Please see my [comment above](http://stackoverflow.com/questions/20747288/parsejsonresp-if-resp-is-number-it-works?noredirect=1#comment31089299_20747288). When you do `if (json) {`, the `0` value is falsey, just like `null`. — cookie monster, Dec 23 '13 at 16:51
@cookiemonster I thought I had major inconsistency at hand :P — , Dec 23 '13 at 16:53
Just FYI, in JavaScript, the falsey values are `null`, `undefined`, `0`, `NaN`, `false` and `""` *(empty string)*. — cookie monster, Dec 23 '13 at 16:55

Alex · Answer 1 · 2013-12-23T16:30:53.963

2

If you're expecting an integer, use parseInt:

try {
    val = parseInt(resp, 10);

    if(val > 0) /* act accordingly ... */
} catch (error) {
    val = null;
}

If you want to know if the "JSON is valid," you can use something akin to the following:

function isValidJSON(string){
    try { 
        $.parseJSON(string);
        return true;
    }
    catch(e){ return false; }
}

edited Dec 23 '13 at 16:30

answered Dec 23 '13 at 16:25

Alex

34,899
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I'm not expecting an integer. I use integers for error messages. – Dec 23 '13 at 16:26
3

@salivan Use HTTP error code for that ! Don't send an error message in place of a data value ! – Denys Séguret Dec 23 '13 at 16:27
@dystroy: Sometimes errors are internal messages that are not HTTP or REST related. – cookie monster Dec 23 '13 at 16:28
@cookiemonster exactly my case. – Dec 23 '13 at 16:29
@cookiemonster 1) http error codes include server error. 2) if it's not enough, if semantically the error is part of the message, data can **contain** the error : `{"error":34}`. A sane protocol shouldn't use polymorphic data where the signification is deduced from the type of the value. – Denys Séguret Dec 23 '13 at 16:30
1

I agree with @dystroy that such errors should be communicated as part of a structure as he shows instead of just a plain number. – cookie monster Dec 23 '13 at 16:31
@dystroy agreed. Will do that in my next app :) – Dec 23 '13 at 16:33
Regarding your second example, I'm doing exactly the same thing. And it is giving me trouble. – Dec 23 '13 at 16:44

score 1 · Answer 2 · answered Dec 23 '13 at 16:30

1

I suggest something like:

// source from Angular source
function isJson(data) { 
  return (/^\s*[\[\{]/.test(data) && /[\}\]]\s*$/.test(data));
};

So...

if (isJson(resp))
  json = $.parseJSON(resp);
else
  alert ('another response: ' + resp);

answered Dec 23 '13 at 16:30

Paul Rad

4,820
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score 0 · Answer 3 · edited May 23 '17 at 11:46

0

Numbers like 2 or 3 are technically valid JSON data. Do you expect an object? See e.g. this SO post for methods of checking if the returned variable is an object.

Basically your workflow would be to try to parse it as JSON, and if it succeeds, check if it's an object/list (depending on what you expect).

Example:

try {
    json = $.parseJSON(resp);
    return (typeof(json) === "object")
} catch (error) {
    json = null;
}

edited May 23 '17 at 11:46

Community

1
1

answered Dec 23 '13 at 16:24

Uli Köhler

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A number doesn't make, according to the spec, a valid message : *"JSON-text = object / array"* – Denys Séguret Dec 23 '13 at 16:25
@dystroy This is true in respect to the JSON spec, but Javascript doesn't handle it that way. E.g. execute `JSON.parse("3")` in Node.JS, it yields 3. – Uli Köhler Dec 23 '13 at 16:26
@UliKöhler: But it doesn't handle `"0"` any differently than `"2"` or `"3"`. – cookie monster Dec 23 '13 at 16:27
@cookiemonster Do you think parsing "0" is the main problem here? I assumed the main question here is how to see the difference between numbers (including "0") and "JSON" (probably objects). To me, "0" returning false is just a sidenote. – Uli Köhler Dec 23 '13 at 16:32
I was only responding to your answer where you say that numbers like `2` or `3` are technically valid. Numbers like `0` aren't any different. We don't know what the actual issue is because `0` will not give `null` in the example in the question. – cookie monster Dec 23 '13 at 16:37

$.parseJSON(resp); if resp is number it works

3 Answers3