Tryit Editor v2.9

Edit This Code:
<!DOCTYPE html>
<html>
<body>

<p>Remove the comment (at the beginning of the lines) to test each case:</p>

<p id="demo"></p>

<script>
var x = 5;
//x = 5 + 7;      // x.valueOf() is 12, typeof x is a number
//x = 5 + "7";    // x.valueOf() is 57, typeof x is a string
//x = "5" + 7;    // x.valueOf() is 57, typeof x is a string
//x = 5 - 7;      // x.valueOf() is -2, typeof x is a number
//x = 5 - "7";    // x.valueOf() is -2, typeof x is a number
//x = "5" - 7;    // x.valueOf() is -2, typeof x is a number
//x = 5 - "x";    // x.valueOf() is NaN, typeof x is a number

document.getElementById("demo").innerHTML = x.valueOf() + " " + typeof x;
</script>

</body>
</html>