Semicolons ;

Semicolons separate JavaScript statements. Add a semicolon at the end of each executable statement:
    <script>
        a = 1;
        b = 2;
        c = a + b;
        document.getElementById("demo1").innerHTML = c;
    </script>

When separated by semicolons, multiple statements on one line are allowed:
    <script>
        a = 1; b = 2; c = a + b;
        document.getElementById("demo1").innerHTML = c;
    </script>

On the web, you might see examples without semicolons. Ending statements with a semicolon is not required, but it is highly recommended.