Values, Types, and Operators

Numbers

JavaScript uses 64 bits to store a single number value. This gives you about 18 quintillion integers, though precision gets tricky with very large numbers. Fractional numbers (like 9.81) are approximations — don't rely on them for exact comparisons.

Special numbers: Infinity, -Infinity, and NaN (Not a Number). NaN is the only value in JavaScript that is not equal to itself.

Strings

Strings can be quoted with backticks, single quotes, or double quotes. Template literals (backtick strings) can span multiple lines and embed expressions with ${}. Strings are immutable and use Unicode under the hood.

The + operator concatenates strings when either operand is a string — a common source of bugs.

Boolean Values

Two values: true and false. Comparison operators (>, <, ==, ===) produce booleans. === avoids type coercion and is almost always what you want.

Logical operators: && (and), || (or), ! (not). They use short-circuit evaluation — || returns the first truthy value, && returns the first falsy value.

Empty Values

null and undefined both represent "no value," but they're used differently. undefined means a value hasn't been assigned. null is typically used as an intentional "no value."

typeof null returns "object" — a famous JavaScript bug that will never be fixed for backward compatibility.