JavaScript/PHP string equality

Question

I'm running an Ajax call which has a success function which takes in a variable returned from the PHP page like so.

Ajax:

$.ajax ({
    type: "POST",
    url: "loginrequest.php",
      data: 'username=' + username + '&password=' +pass,
    success: function(html){
        console.log(html); // Returns login
        console.log(typeof html); // Returns string
        console.log(html === "login"); // Returns false

        if(html === 'login'){
            window.location.href = 'index.php';
        }
        else if(html === 'false'){
            alert("login failed");
        }
    }
});

PHP:

if($count == 1){
    $_SESSION['user'] = $myusername;
    $return = "login";
    echo json_encode($return);
}
else {
    $return = "false";
    echo json_encode($return);
}

As you can see, I'm trying to implement a simple login page and then redirect the user or display an alert depending on the outcome of the number of rows returned from my database query.

What I don't understand is this:

console.log(html); // Returns "login"
console.log(typeof html); // Returns string
console.log(html === "login"); // Returns false

I tried echo-ing without json_encode() and it still would give me the same results. I was using ==, but then I read that it's safer to use ===, so I switched to that, but it still won't return true.

To fix the immediate issue, try console.log(html.trim() === "login");. trim() removes the additional whitespace which can be appended to the response when dealing with plain text. As an improvement, return JSON instead to avoid the problem entirely. — Rory McCrossan
– Rory McCrossan, Commented Jul 4, 2016 at 14:22
json_encode adds " to the string, so you actually have "login" with the quotes. Take a look: https://eval.in/600312 — FirstOne
– FirstOne, Commented Jul 4, 2016 at 14:22
A quick var_dump of the generated 'json' would've easily showed the problem ;) — FirstOne
– FirstOne, Commented Jul 4, 2016 at 14:33

Peter Mortensen · Accepted Answer · 2020-04-03 13:25:44Z

4

You're sending JSON, which means that you're sending the literal bytes:

"login"
"false"

Note the quotes in there. Your JavaScript code either needs to decode the JSON, or compare the raw JSON itself:

 result = JSON.parse(html)
 if (result == "login")

or

 if (html == '"login"')   // Note the quotes

A simple console.log(html) would have shown you what you're dealing with.

edited Apr 3, 2020 at 13:25

Peter Mortensen

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answered Jul 4, 2016 at 14:24

Marc B

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2 Comments

FirstOne Over a year ago

From the question, the op actually did run console.log(html); // returns "login", but they probably thought it was how the console displays strings... xD

Marc B Over a year ago

json is a string. plain and simple. that's the whole point of it. encoding arbitrary JS data structures/types into a simple string for transport. raw json received via http will always be a string.

Peter Mortensen · Accepted Answer · 2020-04-03 13:28:34Z

1

If you are using json_encode on the PHP side then you should use:

jQuery.parseJSON on the JavaScript side -

html = jQuery.parseJSON(html);

edited Apr 3, 2020 at 13:28

Peter Mortensen

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answered Jul 4, 2016 at 14:25

RIYAJ KHAN

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