The == and != operators do type coercion before comparing. This is bad because it causes ' \f\r \n\t ' == 0 to be true. This can mask type errors.

When comparing to any of the following values, always use the === or !== operators, which do not do type coercion:

0 '' undefined null false true

If you want the type coercion, then use the short form. Instead of:

(foo != 0)

just say:

(foo)

And instead of:

(foo == 0)

say:

(!foo)

Use of the === and !== operators is always preferred. There is a "Disallow == and != " (eqeqeq) option, which requires the use of === and !== in all cases.