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Short circuit in JavaScript | Example code

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There are 2 Short Circuit Conditionals in JavaScript first using && (And logic) and another one is Evaluation with || (OR logic).

Logical AND (&&)

The logical AND (&&) operator (logical conjunction) for a set of boolean operands will be true if and only if all the operands are true. Otherwise, it will be false.

expr1 && expr2

Logical OR (||)

The logical OR (||) operator (logical disjunction) for a set of operands is true if and only if one or more of its operands is true. I

expr1 || expr2

Short circuit in JavaScript

A simple example code is evaluating an AND expression (&&), if the first operand is false, JavaScript will short-circuit and not even look at the second operand.

true && true
// true

true && false
// false

false && false
// false

Code

<!DOCTYPE html>
<html>
<body>

  <script>
    const a = 3;
    const b = -2;

    console.log(a > 0 && b > 0);
  </script>

</body>
</html
>

Output:

Short circuit in JavaScript

Expressions – Logical OR

const a = 3;
const b = -2;

console.log(a > 0 || b > 0);
// expected output: true

Does JavaScript have a “Short-circuit” evaluation?

Answer: Yes, JavaScript has a “short-circuit” evaluation like && Operator in C#.

  • (some falsy expression) && expr will evaluate to falsy expression
  • (some truthy expression) || expr will evaluate to a truthy expression
if (true == true || foo.foo){
    // Passes, no errors because foo isn't defined.
}

Do comment if you have any doubts or suggestions on this JS short circuit topic.

Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.

OS: Windows 10

Code: HTML 5 Version

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