json_encode result not readable by JSON.parse

Question

With php I use json_encode to encode some values from a json array. These values are needed in a javascript file.

I noticed that php json_encode gives a string surrounded by square brackets "[ ]" and these brackets are not accepted by JSON.parse in javascript.

If I replace the square brackets by curly brackets "{ }" then JSON.parse is working fine.

json1 = '{"4":{"eng":"2","deu":"2"}}'; // json with curly brackets (works fine)
json2 = '["4":{"eng":"2","deu":"2"}]'; // json with square brackets (does not work)

test1  = validateJson( json1 ); // valid json
test2  = validateJson( json2 ); // invalid json

function validateJson( str ) {

    let tmp;

    try { tmp = JSON.parse( str ); } catch ( e ) {

        console.error( 'INVALID JSON ' + str );

        return false;
    
    }

    return tmp;

}

I don't know what the best solution is. Why are php json_encode and javascript JSON.parse not compatible? Is it json_encode who gives incorrect json? Or is it JSON.parse that can't read json properly?

In your opinion should I modify the json string server-side in php before sending it to javascript? Or should I rather find an alternative to JSON.parse? Do you have an idea what is the best thing to do? Any suggestion is welcome

Here is a complete example, if I visit this page there will be a javascript error in the console, which I don't understand why because this json seems valid:

<html>
<body>
<script>

    json1 = '{"4":{"eng":"2","deu":"2"}}'; // json with curly brackets (works fine)
    json2 = '["4":{"eng":"2","deu":"2"},"5":{"eng":"3","deu":"3"}]'; // json with square brackets (does not work)

    test1  = validateJson( json1 ); // valid json
    test2  = validateJson( json2 ); // invalid json

    function validateJson( str ) {

        let tmp;

        try { tmp = JSON.parse( str ); } catch ( e ) {

            console.error( 'INVALID JSON ' + str );

            return false;
        
        }

        return tmp;

    }

</script>

</body>
</html>```

Thank you very much :)

Square brackets most definitely are accepted by `JSON.parse()` in JavaScript. The problem is that your square brackets syntax is incorrect. Square brackets are for *arrays*. — Pointy, Mar 07 '21 at 02:40
that's weird wondering why does the console throw an error then? if it's for arrays i'm gonna try this, thank you hopefully it'll work — LesDentsDeLaMer, Mar 07 '21 at 02:41
Your syntax is wrong. You need to post more relevant code; JSON encoding and decoding libraries are generally completely compatible because the syntax is so simple, and that's *certainly* true between PHP and JavaScript. — Pointy, Mar 07 '21 at 02:43
@Pointy, "your square brackets syntax is incorrect" you are probably right however i don't understand how to overcome this issue, because this syntax is generated by php with json_encode — LesDentsDeLaMer, Mar 07 '21 at 03:02
How are you returning JSON to JS? Using AJAX? Try console.log(json 2) without JSON.parse. Most probably its already JSON. You don't need JSON.parse. — Vinay Kharayat, Mar 08 '21 at 14:22

json_encode result not readable by JSON.parse

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