What happens?

The browser HTML parser will see the </script> within the string and it will interpret it as the end of the script element.

Look at the syntax coloring of this example:

<script>

var test = 'foo... </script> bar.....';

</script>

Note that the word bar is being treated as text content outside of the script element...

A commonly used technique is to use the concatenation operator:

var test = '...... </scr'+'ipt>......';