<div id="home-slogan">

<?php

    $filename = "testimonials/testimonial.txt"; #specify file
    $file = fopen($filename, "r");              #open file
    $numLines = count(file($filename));         #count number of lines
    $lines = file($filename);                   #read lines into array
    $randomTestimonial = rand(0,$numLines);     #generate random number
?>

<h1 id="heading" align="center">"<?php echo $lines[$randomTestimonial];?>"</h1>
<button type="button" id="next">Next Testimonial</button>

<script>

    var randomTestimonial = <?php echo $lines[$randomTestimonial];?>;

    $("#next").click(function(){
    $("#heading").replaceWith(randomTestimonial);
    });

</script>