Json.parse considers number as a string as valid json object

Question

const isJson = ( str ) => {
    try {
        var res = JSON.parse( str );

    } catch ( e ) {
        return false;
    }
    return true;
};

console.log(isJson('W-11'));

This code returns false.

const isJson = ( str ) => {
    try {
        var res = JSON.parse( str );

    } catch ( e ) {
        return false;
    }
    return true;
};

console.log(isJson('123'));

This returns true.

Need to know why json.parse treats pure number as string a valid json and string with character not valid json. Apologies if it is a newbie question.

Possible duplicate of [How to escape special characters in building a JSON string?](https://stackoverflow.com/questions/19176024/how-to-escape-special-characters-in-building-a-json-string) — MrMaavin, Oct 25 '18 at 05:48

score 1 · Accepted Answer · answered Oct 25 '18 at 06:10

JSON is a text representation of some data structure (usually an array or an object) but primitive values like strings, numbers and boolean values can also be encoded as JSON (and successfully decoded).

Assuming both strings you want to decode were valid JSON, the code that produces them should look like:

var x = 123;
var a = JSON.stringify(x);
// a == '123'

var y = W-11;
var b = JSON.stringify(y);
// b != 'W-11'

If you try to run this code, the statement y = W-11 triggers a ReferenceError ("W is not defined").
Or, if the W variable is defined, W-11 is a subtraction that tries to convert W to a number and the result is a number (or NaN).

Either way, it is impossible to generate W-11 using JSON.stringify() (because it is not valid JSON). What you probably want is to parse the string "W-11" and get W-11 as the value encoded to produce it:

console.log(JSON.parse('"W-11"'));
// W-11

Your confusion comes from the fact that in the JavaScript code the strings are surrounded by quotes or apostrophes. This is how the interpreter knows that the characters between the quotes represent themselves and they must not be interpreted as code.
In code, 'W-11' is a string encoded as JavaScript while the actual value of the string is W-11 (no quotes). You can also write it in JavaScript code as as "W-11" or `W-11`.

Not sure the explanation with the "code to produce this should look like this" example is really useful. I'd say the other way around: `123` means something useful in Javascript, but a bare `W-11` does not for the same reason as it doesn't in JSON. — deceze, Oct 25 '18 at 06:51

score 0 · Answer 2 · answered Oct 25 '18 at 05:42

Is a valid JSON literal value. JSON supports number literals, and this is one.

W-11

This is invalid JSON. The characters W and - have no meaning in the JSON spec (well, - would be part of negative number literals, but anyway…). If you want to form a JSON string literal, this would be one:

"W-11"

So:

JSON.parse('"W-11"')  // ok

The contents of your Javascript string must be valid JSON. W-11 isn't a string to JSON, only "W-11" is.

score 0 · Answer 3 · answered Oct 25 '18 at 05:42

0

If you want 'W-11' to work pass it like this '"W-1"' in isJSON function

If it's doublequoted then it's a string else it's a numeric, boolean, null.

answered Oct 25 '18 at 05:42

Atishay Jain

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Json.parse considers number as a string as valid json object

3 Answers3