Preserving order of an associative PHP array while passing it to javascript through ajax

Question

So Here is my php file code

GetUserArray.php

$Users = array('7'=>'samei', '4'=>"chaya", '10'=>'abetterchutia');
echo json_encode($Users);

and this is my ajax request

 $.ajax({
             url: './GetUserArray.php',
             type: 'POST',
             dataType: "json",
             success: function(users) {
                 console.log(users);
                 $.each( users, function( key, value ) {
                 console.log(key, value);
               });
             }

         });

now what it gives me is in the console is an object sorted by the keys of that array while i want the orignal order which was 7 4 10 in my php file

Object {4: "chaya", 7: "samei", 10: "abetterchutia"}
4 chutiya
7 sali
10 abetterchutia

Answer 1

The problem with using hashmaps is that they don't actually specify order. Though, in PHP, an array is actually an ordered hashmap, so it does. Once you translate that into an object in Javascript, the order is no longer preserved. The only way to guarantee order in Javascript is to use an array.

So in PHP this works as expected and preserves order.

$arr = [4 => "I'm first", 1 => "I'm second", 3 => "I'm third"];

foreach($arr as $value) {
    echo $value, "\n";
}

Which gives us

I'm first
I'm second
I'm third

But encode that to Javascript Object Notation (i.e. JSON) and you get an object, because in Javascript arrays don't have keys, they have indexes.

echo json_encode($arr);

Gives us...

{"4":"I'm first","1":"I'm second","3":"I'm third"}

If you tried to do the same in Javascript with this object you might not get the same order

var obj = {"4":"I'm first","1":"I'm second","3":"I'm third"};

var s = "";
for(var x in obj) {
    s += + obj[x] + "\n";
}

document.write("<pre>" + s + "</pre>");

This might give you something more like...

I'm second
I'm third
I'm first

So the only way to fix that is to use an array...

json_encode(array_values($arr));

Now this gives us...

["I'm first","I'm second","I'm third"]

And the order is maintained.

However, if you want to preserve the keys as well, you'll have to create an array of objects.

$json = [];
foreach($arr as $key => $value) {
    $json[] = [$key => $value];
}

echo json_encode($json);

Now you get...

[{"4":"I'm first"},{"1":"I'm second"},{"3":"I'm third"}]

Which in javascript, works perfectly as expected...

for(var x in obj) {
    for(var n in obj[x]) {
        obj[x][n]; // now you can both maintain order and have access to the key
    }
}