Why javascript doesn't parse this string?

Question

When I pass json encoded value from PHP to Javascript and just console log it it returns me this:

{"id":"4","username":"muzikant346","coins":"675","avatar1":"1","avatar2":"0","avatar3":"0","avatar4":"0","avatar_selected":"0"}

This is a string and when I want to parse it in Javascript it returns an error:

eUncaught SyntaxError: Unexpected token  in JSON at position 0
at JSON.parse (<anonymous>)
at Object.success (welcome.js:11)
at c (jquery-3.4.1.min.js:2)
at Object.fireWith [as resolveWith] (jquery-3.4.1.min.js:2)
at l (jquery-3.4.1.min.js:2)
at XMLHttpRequest.<anonymous> (jquery-3.4.1.min.js:2)

I don't understand why javascript can't parse this.

There is my PHP (fetch from database) code:

$sql = "SELECT * FROM serbian_values WHERE username = '$username'";
        $result = mysqli_query($link, $sql);
        if($result){
            while($row = mysqli_fetch_assoc($result)){
                $value[] = $row;
            }
            echo json_encode($value[0]); 
        }

Danger: You are vulnerable to SQL injection attacks that you need to defend yourself from. — Quentin
– Quentin, Commented Apr 17, 2020 at 8:04
@AlwaysSunny — No, it doesn't. There is a U+FEFF : ZERO WIDTH NO-BREAK SPACE [BOM] {BOM, ZWNBSP} before the first U+007B : LEFT CURLY BRACKET {left brace}: jsbin.com/xabezuwura/1/edit?html,js,output — Quentin
– Quentin, Commented Apr 17, 2020 at 8:05
obj='{"id":"4","username":"muzikant346","coins":"675","avatar1":"1","avatar2":"0","avatar3":"0","avatar4":"0","avatar_selected":"0"}'; console.log(JSON.parse(obj)); — A l w a y s S u n n y
– A l w a y s S u n n y, Commented Apr 17, 2020 at 8:06
@AlwaysSunny — Of course it works if you delete that character — Quentin
– Quentin, Commented Apr 17, 2020 at 8:07

Quentin · Accepted Answer · 2020-04-17 08:10:39Z

1

A U+FEFF : ZERO WIDTH NO-BREAK SPACE [BOM] {BOM, ZWNBSP} is not a valid character to start a JSON text with.

Somewhere it is getting inserted into the start of the output of the PHP program (or mixed in before parsing in the JS you haven't shown us, but that is less likely).

Possibly this is used by the wrong charset appearing on the Content-Type header you are outputting from PHP, but the character is probably just lurking in the source code somewhere. It would probably be easiest to find with a hex editor.

edited Apr 17, 2020 at 8:10

answered Apr 17, 2020 at 8:02

Quentin

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A l w a y s S u n n y · Accepted Answer · 2020-04-17 08:17:26Z

1

Another way to fix that first BOM character,

function stripBOM(content) {
  content = content.toString()
  if (content.charCodeAt(0) === 0xFEFF) {
    content = content.slice(1)
  }
  return content
}

console.log(JSON.parse(stripBOM(obj)));

Ref. https://gist.github.com/pbakondy/f5045eff725193dad9c7

answered Apr 17, 2020 at 8:17

A l w a y s S u n n y

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1 Comment

A l w a y s S u n n y Over a year ago

Another ref: gist.github.com/antic183/619f42b559b78028d1fe9e7ae8a1352d

Danilo Körber · Accepted Answer · 2020-04-17 08:05:37Z

-1

JSON.parse can only parse string elements. One solution is to stringify your JSON first:

JSON.parse(JSON.stringify({"id":"4","username":"muzikant346","coins":"675","avatar1":"1","avatar2":"0","avatar3":"0","avatar4":"0","avatar_selected":"0"}));

answered Apr 17, 2020 at 8:05

Danilo Körber

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1 Comment

Quentin Over a year ago

If that was the problem, then the error message would be about an unexpected token o and not a zero width non-breaking space.

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