- чувствиетелен к регистру

- не должен начинаться с цифры

- зарезервированные слова

While naming your variables in JavaScript, keep the following rules in mind.

• You should not use any of the JavaScript reserved keywords as a variable name. These keywords are mentioned in the next section. For example, break or boolean variable names are not valid.
• JavaScript variable names should not start with a numeral (0-9). They must begin with a letter or an underscore character. For example, 123test is an invalid variable name but _123test is a valid one.
• JavaScript variable names are case-sensitive. For example, Name and name are two different variables.