Expanding on someone else's answer:

<script>
  var myvar = <?= json_encode($myVarValue, JSON_UNESCAPED_UNICODE); ?>;
</script>

Using json_encode() requires:

• PHP 5.2.0 or greater
• $myVarValue encoded as UTF-8 (or US-ASCII, of course)

Since UTF-8 supports full Unicode, it should be safe to convert on the fly.

Please note that if you use this in html attributes like onclick, you need to pass the result of json_encode to htmlspecialchars(), like the following:

htmlspecialchars(json_encode($string), ENT_QUOTES);

or else you could get problems with, for example, &bar; in foo()&&bar; being interpreted as an HTML entity.

You can use the wp_localize_script to pass a variable to your javascript.

Here is an example:

wp_register_script('your_script_name', 'path/to/script.js');
$variables = array (
    'footer_caption' => $attr['footer_caption'],
);
wp_localize_script('your_script_name', 'js_object_name', $variables );
wp_enqueue_script('your_script_name');

Then you can acces to this variable by:

js_object_name.footer_caption

Use json_encode() to convert any PHP value to the corresponding Javascript literal:

var datestring = <?php echo json_encode($datestring); ?>;

alert('my name is: <?php echo $man; ?>' );

You should just use json_encode() from http://www.php.net/manual/en/function.json-encode.php

Example:

var str1 = <?php echo json_encode($str) ?>;

It takes care of converting newlines to \n, escaping any other special characters as necessary, preserve spaces, etc.

Example output for your string:

var str1 = "\n         this\n         is\n         my\n         string";

Try this:

echo '<td><input id="btnUpdate" type="submit" name="btnUpdate" value = "Update" onclick="updateButton("' . $row['CustomerID']  . '","' .  $row['custEmail'] . '")" /> </td>';

echo"
    <table>
         <p><input type='text' id='newPostComment' value='' placeholder='WRITE YOUR COMMENT HERE...' size='35'/><input type='submit' value='UPLOAD' onclick='uploadPostComment(\"$parentID\", \"" . str_replace('"', '\"', $comment) . "\");fetchComment()'/></p>
    </table>

You need to quote the fields. If your field is an integer it does not need to be quoted, if it is a string it needs to be. I quoted both because I don't know if parentID is a string id or a numeric id. Do what your application needs of course.

Update: in regards to Michael's comment about breaking if comment contains a quote. We now escape all double quotes in $comment to prevent that.

The value of the onclick attribute should be escaped like any other HTML attribute, using htmlspecialchars(). Actual Javascript strings inside the code should be encoded using json_encode(). For example:

<?php
$message = 'Some \' problematic \\ chars " ...';
$jscode = 'alert('.json_encode($message).');';
echo '<a onclick="' . htmlspecialchars($jscode) . '">Click me</a>';

That being said... onclick (or any other event) attributes are so 2005. Do yourself a favor and separate your javascript code from your html code, preferably to external file, and attach the events using DOM functions (or jQuery, which wraps it up nicely)

Change your Line 5 - Line 7 code to:

echo '<div class="FloorH">
            &nbsp;First Floor <button onclick="changeBG(\'' . $floorDiv . '\',\'#F0F\');">Magenta</button>
      </div>';

because PHP will not parse variable inside single quote quoted string .

More detail of variable parsing within double quotes string you can check out this php documentation variable parsing

<?php
  $test = array('2015-10-05','20151005');
  echo $test[0]."<br>";
  echo $test[1];
  echo '<script>localStorage["test1a"] = "'.$test[0].'";</script>';
  echo '<script>localStorage["test2a"] = "'.$test[1].'";</script>';
?>
<script>localStorage["test1b"] = "2015-10-05";</script>
<script>localStorage["test2b"] = "20151005";</script>

Note the Additional Quotes added '"' wrapping the array variable. To explain why it does not store the value but calculate it is because you are throwing a string at browser and it interpretes as HTML or Javascript in this case.

$page = 
"<script type=\"text/javascript\"> 

function outf(text) { 
    var mypre = document.getElementById(\"output\"); 
    mypre.innerHTML = mypre.innerHTML + text; 
} 
function builtinRead(x) {
    if (Sk.builtinFiles === undefined || Sk.builtinFiles[\"files\"][x] === undefined)
    throw \"File not found: '\" + x + \"'\";
    return Sk.builtinFiles[\"files\"][x];
}

function runit() { 
    var prog = document.getElementById(\"yourcode\").value; 
    var mypre = document.getElementById(\"output\"); 
    mypre.innerHTML = ''; 
    Sk.canvas = \"mycanvas\";
    Sk.pre = \"output\";
    Sk.configure({output:outf, read:builtinRead}); 
try {
    eval(Sk.importMainWithBody(\"<stdin>\",false,prog)); 
}
catch(e) {
    alert(e.toString())
}
} 
</script>";

<?php
fwrite($fh, $page); 
?>

The best way IMHO would be this:

tagName: <?php echo json_encode($tagged); ?>

This way, you don't have to take care of escaping quotes, escape characters or other unwanted signs.