Cookies Javascript / PHP

Question

I made like / dislike buttons in a news feed (like Facebook). I want to change the database when someone clicks on either one of those buttons using PHP. I first made the two buttons in a form but then the PHP would be run on a different page and reload the first page causing you to go back to the top of the news feed (which of course shouldn't happen). Then I tried Javascript, but I needed to pass the id of the post from Javascript to PHP. I tried doing this with Cookies:

document.cookie= and $_COOKIE[]

function like(id) {
    document.cookie="lid="+id;
    <?php query("INSERT INTO `likes`(`uid`, `pid`) VALUES (".$_SESSION['id'] . ",".$_COOKIE['lid'].")"); ?>
}
function dislike(id) {
    document.cookie="lid="+id;
    <?php query("DELETE FROM `likes` WHERE uid=".$_SESSION['id'] . " AND pid=".$_COOKIE['lid']); ?>
}

This didn't work so I added some alerts to understand what was going on.

function like(id) {
    <?php $_COOKIE['lid'] = "10"; ?>
    alert("Like:" + id);
    document.cookie="lid="+id;
    <?php query("INSERT INTO `likes`(`uid`, `pid`) VALUES (".$_SESSION['id'] . ",".$_COOKIE['lid'].")"); ?>
    alert("<?php echo $_COOKIE['lid']; ?>");
}
function dislike(id) {
    <?php $_COOKIE['lid'] = "10"; ?>
    alert("Dislike:" + id);
    document.cookie="lid="+id;
    <?php query("DELETE FROM `likes` WHERE uid=".$_SESSION['id'] . " AND pid=".$_COOKIE['lid']); ?>
    alert("<?php echo $_COOKIE['lid']; ?>");
}

The first alert showed the correct id, but the second alert showed "10".

What did I do wrong?

How should I transfer the id from JavaScript to PHP?

Is there an other good way to run PHP code when someone clicks on a button without the newsfeed going back to the top?

Thanks

powerc9000 · Accepted Answer · 2017-04-11 16:42:35Z

1

Javascript isn'g going to run PHP.

What happens is the PHP code is run before the page is sent to the user.

After the PHP is interpreted.

before

function dislike(id) {
    <?php $_COOKIE['lid'] = "10"; ?>
    alert("Dislike:" + id);
    document.cookie="lid="+id;
    <?php query("DELETE FROM `likes` WHERE uid=".$_SESSION['id'] . " AND pid=".$_COOKIE['lid']); ?>
    alert("<?php echo $_COOKIE['lid']; ?>");
}

after (what gets sent to the user)

function dislike(id) {
    alert("Dislike:" + id);
    document.cookie="lid="+id;
    alert("10"); //whatever that cookie id was
}

So the code <?php query("DELETE FROM `likes` WHERE uid=".$_SESSION['id'] . " AND pid=".$_COOKIE['lid']); ?> has already run by the time the user sees the page and so the like is deleted

You need to user AJAX to properly do this.

function dislike(id){
    var XHR = new XMLHttpRequest();
    XHR.addEventListener("load", function(){
        //was disliked
    })
    XHR.open("get", "dislike.php?id="+id);
    XHR.send();
}

something like unto that for javascript

dislike.php

<?php
parse_str($SERVER["QUERY_STRING"], $arr);
if(isset($arr["id"]){
 query("DELETE FROM `likes` WHERE uid=".$_SESSION['id'] . " AND pid=".$arr["id"]);
}

answered Apr 11, 2017 at 16:42

powerc9000

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3 Comments

Martin W Over a year ago

It's not working. Nothing happens. I don't understand: XHR.addEventListener("load", function(){ //was disliked })

powerc9000 Over a year ago

That's the callback that is run when the server returns.

Martin W Over a year ago

Nothing happens ...the code doesn't work. Please help

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