Inserted double quote when prepending to the_content

Question

I am trying to write a plug-in to display the RunKeeper Healthy button on single posts, but my output has an extra space and double-quote when I look at the page source. What I'm trying to do with the button is open a new window via inline JavaScript.

I've tried switching between single and double quotes and have also ensured that I was escaping nested quotes properly. Trying to append the get_permalink() breaks the generated link for the RunKeeper sharing URL. The image tag for the link itself is fine, but I see an incomplete link when I hover over it.

The link output is:

<a href="javascript:void(window.open('http://runkeeper.com/share?healthyUrl=http://my_website/my_post_permalink/ " , '' , 'width=630,height=350');">

But what I would expect is:

<a href="javascript:void(window.open('http://runkeeper.com/share?healthyUrl=http://my_website/my_post_permalink/' , '' , 'width=630,height=350');">

This is what my plug-in code is so far:

add_filter('the_content', 'add_runkeeper_btn' );

function add_runkeeper_btn($content) {
    $output = "";

    if (is_single()) {
        $output .= "<a href=\"javascript:void(window.open('http://runkeeper.com/share?healthyUrl=";
        $output .= get_permalink();
        $output .= "', '' , 'width=630,height=350');\">";
        $output .= "<img src=\"http://runkeeper.com/static/kronos/images/HealthyButton.png\" class=\"healthyImage\" alt=\"RunKeeper Healthy Button\" />";
        $output .= "</a>";
    }

    return $output . $content;
}

For reference this is what is in the page source of the RunKeeper blog post. I am trying to modify it so that the healthyUrl query parameter references the permalink for the post.

<a href="javascript:var%20d=document,l=d.location;void(window.open('http://runkeeper.com/share?healthyUrl='%20+%20l.href,'','width=630,height=350'));">
    <img src="http://runkeeper.com/static/kronos/images/HealthyButton.png" class="healthyImage" alt="RunKeeper Healthy Button">
</a>

Answer 1

You fixed it by changing the double quote to a single quote. :)

<a href="javascript:void(window.open('http://runkeeper.com/share?healthyUrl=http://my_website/my_post_permalink/ " , '' , 'width=630,height=350');">
                                                                                                               ^^^^^

You happened to fix it by refactoring with the "echo" statements. :D

Answer 2

I fixed this by switching the string concatenation to use PHP's echo instead of doing string concatenation. I also noticed I had a missing parenthesis in my original code (which didn't affect the result of the output where the single quote was turned into a double-quote).

I still have no idea why I was getting a single quote replaced by a double quote even if I had split up the reference code from RunKeeper's blog post.

Here is my final function:

function add_runkeeper_btn($content) {
    if (is_single()) {
        echo '<p><a href="javascript:void(window.open(\'http://runkeeper.com/share?healthyUrl=';
        echo trim(get_permalink());
        echo '\', \'\', \'width=630,height=350\'));">';
        echo '<img src="http://runkeeper.com/static/kronos/images/HealthyButton.png" class="healthyImage" alt="RunKeeper Healthy Button" />';
        echo '</a></p>';
    }

    return $content;
}