Pass a PHP variable to a JavaScript variable

What is the easiest way to encode a PHP string for output to a JavaScript variable? I have a PHP string which includes quotes and newlines. I need the contents of this string to be put into a JavaScript variable. Normally, I would just construct my JavaScript in a PHP file, à la: <script> var myvar = "<?php echo $myVarValue;?>"; </script> However, this doesn't work when `$myVarValue` contains quotes or newlines.