PHP Encode JavaScript String; encode double quotes, single quotes; onclick parameter

function js_escape($str) {
    for ($i = 0, $l = strlen($str), $new_str = ''; $i < $l; $i++) {
        $new_str .= (ord(substr($str, $i, 1)) < 16 ? '\\x0' : '\\x') . dechex(ord(substr($str, $i, 1)));
    }
    return $new_str;
}

$var = '"Convinced myself, I seek not to convince." -Edgar Allan Poe';

<input value="Click me" onclick="doSomething('<?php echo js_escape($var); ?>');" type="button" />
<!--
<input value="Click me" onclick="doSomething('\x22\x43\x6f\x6e\x76\x69\x6e\x63\x65\x64\x20\x6d\x79\x73\x65\x6c\x66\x2c\x20\x49\x20\x73\x65\x65\x6b\x20\x6e\x6f\x74\x20\x74\x6f\x20\x63\x6f\x6e\x76\x69\x6e\x63\x65\x2e\x22\x20\x2d\x45\x64\x67\x61\x72\x20\x41\x6c\x6c\x61\x6e\x20\x50\x6f\x65');" type="button" />
-->