Logical AND (&&) Expression

Summary

Evaluates from left to right. If the first expression evaluates to a falsy value, it is returned; otherwise, the evaluated value of the second expression is returned. This expression can be used to combine conditions in if statements and other conditional statements.

Syntax

expression1 && expression2

Parameters

expression1: Any legal expression.
expression2: Any legal expression.

Description

&& is the logical AND operator. If the first expression evaluates to false (or a "falsy" value), it is returned; otherwise, the evaluated value of the second expression is returned. In the case of Boolean expressions, this yields the expected result of true if both expressions are true, and false otherwise. However, with other data types, the output may be non-Boolean. For example, true && "blue" yields "blue".

The && operator is evaluated from left to right.

Using && to test more than one condition in an if statement

The logical AND operator can be used to combine conditions and test if both conditions are true, such as for if statements:

import System;
 
bool x = true, y = true;
if (x && y) {
    Console.log("'x' and 'y' are both true");
}

Short-Circuit Evaluation

If the expression prior to an && operator is false, then the expression is, if well-formed, false. In such cases JS++ does not evaluate the expression following &&.

While this "short-circuiting" is logically sound, it means that side effects of the expression after the operator are not executed. For example:

int x = 0, y = 0;
if ((3 < 2) && x++) { // does not iterate x because of short-circuiting
    y = 1;
}
(3 > 2) && x++; // iterates x
 
// final result is x = 1 (iterated once) and y = 0

Care must therefore be taken when the expressions following logical operators are expected to have side effects.