Logical Operators2026-04-04

Logical operators in JavaScript do more than return true or false. They return actual values, and they stop evaluating as soon as the result is known.

|| OR

|| returns the first truthy value it finds. If every value is falsy, it returns the last value in the chain.

This is useful for defaults:

const displayName = user.name || "Anonymous";

If user.name is an empty string, || treats it as missing and falls back to "Anonymous".

&& AND

&& returns the first falsy value it finds. If every value is truthy, it returns the last value.

It is often used to guard execution:

isLoggedIn && showDashboard();

When the left side is falsy, JavaScript stops immediately and does not evaluate the rest.

! NOT

! converts a value to a boolean first, then flips it.

!"hello"; // false
!0; // true

Because it forces boolean conversion, !!value is a common shortcut for turning any value into a strict boolean.

?? Nullish Coalescing

?? returns the first value that is not null and not undefined.

This is a safer defaulting operator than || when 0, false, or "" are valid values:

const result = a ?? b;

That is equivalent to:

const result = a !== null && a !== undefined ? a : b;

Use || when you want to reject all falsy values. Use ?? when only null and undefined should trigger the fallback.

Precedence

! has the highest precedence of the logical operators, then &&, then ||.

If you mix && and ||, parentheses make the intent explicit:

(a && b) || (c && d);

?? is separate from || and && in practice, so it is best to parenthesize mixed expressions to keep the logic obvious.

Summary

• || finds the first truthy value.
• && finds the first falsy value.
• ! converts to boolean and flips it.
• ?? finds the first defined value.

These operators are about control flow as much as comparison. The returned value matters.