If you are using the values on a page (e.g. the values of form elements) directly in mathematical formulas in javascript, you can have issues with ambiguity of types. For instance:

    var total = 0;
    total += document.myForm.element.value;  // e.g. value = 5
    alert(total);

The above example can lead to a result of “05″ instead of “5″ as the browser may interpret the two values as strings. To avoid this, use the Number() function to cast the string as a number:

    var total = 0;
    total += Number(document.myForm.element.value);
    alert(total);

You can also cast a number to a string by using the String() function. See more here.