JavaScript Variable Naming

The rules

A variable name can contain letters, digits, _ and $. It must follow these rules:

• It cannot start with a digit: 2fast is invalid, fast2 is fine.
• It cannot contain spaces or hyphens: my-name is invalid.
• It cannot be a reserved word such as let, class, return or function.
• It is case sensitive: total and Total are different.

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const userName = "Maya";
const _private = 1;
const $element = "dollar names are allowed";
const total2 = 5;
console.log(userName, _private, $element, total2);

Use camelCase

The JavaScript convention is camelCase: the first word is lower case and each following word starts with a capital.

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const firstName = "Maya";
const totalPrice = 120;
const isLoggedIn = true;

Other conventions exist for other jobs: PascalCase for classes (ShoppingCart) and UPPER_SNAKE_CASE for true constants that are known before the program runs (MAX_ITEMS).

Good names say what a value is

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// Hard to read
const d = 7;
const x = d * 24;

// Clear
const daysInWeek = 7;
const hoursInWeek = daysInWeek * 24;

A few habits that help:

• Use whole words: index, not idx, unless it is a very common short name such as i in a small loop.
• Name booleans like questions: isOpen, hasError, canEdit.
• Name arrays with plural words: users, prices. Name a single item in the singular: user.
• Avoid misleading names: list should hold a list.