In JavaScript, short-circuit evaluation in the logical AND operator refers to the fact that if the first part of a logical AND expression (e.g. "a" in a && b) evaluates to false, then the second part of the expression is not evaluated. This means that if the left operand is a falsy value, then the operand on the right is never evaluated.
In cases where the expression short-circuit evaluates to false, the operand that evaluated to false is the one that is returned. To illustrate this, consider for example, the following:
console.log(false && true); // false console.log(1 && null && 'never reaches here'); // null console.log([].length && true); // 0
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