Logical operators in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the logical AND operator (&&) do in JavaScript?

The logical AND operator (&&) returns true if both values on its sides are true. If either side is false, it returns false.

beginner

What is the result of true || false in JavaScript?

The result is true because the logical OR operator (||) returns true if at least one side is true.

beginner

Explain the logical NOT operator (!) in JavaScript.

The logical NOT operator (!) reverses the truth value. If the value is true, it becomes false; if false, it becomes true.

intermediate

What will false && (anything) evaluate to and why?

It will evaluate to false immediately because with AND, if the first value is false, the whole expression is false without checking the second value.

intermediate

How does short-circuit evaluation work with logical OR (||)?

With OR (||), if the first value is true, JavaScript does not check the second value because the whole expression will be true anyway.

What is the result of true && false?

A true

B false

C undefined

D null

AND (&&) returns true only if both sides are true. Here, one side is false, so the result is false.

Which operator returns true if at least one operand is true?

A ||

B !

C &&

D ===

The OR operator (||) returns true if either operand is true.

What does the expression !false evaluate to?

A true

B false

C null

D undefined

The NOT operator (!) reverses the value, so !false becomes true.

In false && someFunction(), will someFunction() be called?

A Only if someFunction returns false

B Yes, always

C Only if someFunction returns true

D No, because of short-circuit

With AND, if the first value is false, JavaScript skips evaluating the second value (short-circuit).

What is the result of true || false?

A null

B false

C true

D undefined

OR (||) returns true if at least one operand is true.

Explain how the logical AND (&&) and OR (||) operators work in JavaScript, including short-circuit behavior.

Think about when JavaScript stops checking the second value.

Describe the effect of the logical NOT (!) operator on a boolean value.

It flips the truth value.