Skill Maps

Smart Operators

The && (AND) and || (OR) operators in JavaScript work on the principle of " short-circuiting " . They stop evaluation as soon as the result becomes clear.

1. OR (||) seeks the FIRST TRUTHY

It returns the first true value encountered (or the last value if no truth is found).

let name = username || "Anonymous"; 
// If username is an empty string or null, we assign "Anonymous"

2. AND (&&) seeks the FIRST FALSY

It returns the first false value encountered (or the last value if all are true).

isAdmin && alert("Hello, admin!"); 
// alert will only trigger if isAdmin === true

3. Difference from Nullish (??)

Remember: || considers 0, false, and "" as false. If these values are valid for you, use ??.

Tip

Short-circuiting is often used for safe access to nested properties (before the ?. operator existed): user && user.address && user.address.city.

Caution

Don't make chains too long — such code is hard to read and debug.