When Do JavaScript Logical Operators Return Objects Instead of Booleans?

Logical Operators in JavaScript: Beyond Boolean Results

In JavaScript, while logical operators such as '&&' (AND) and '||' (OR) typically return boolean results, certain circumstances can lead to the return of other objects.

To understand why, it's crucial to grasp the concept of short-circuit evaluation. Both '&&' and '||' are short-circuit operators, meaning they cease evaluating once the logical result is determined.

In the expression 'X || Y', 'X' is evaluated first. If 'X' is determined to be "true", the expression returns 'X' without further evaluation. This is where the "short-circuit" comes into play. On the other hand, if 'X' is "false", 'Y' is evaluated, and the expression returns 'Y'.

Similarly, '&&' operates by returning the first "truthy" argument or the last "falsy" argument.

The catch arises from JavaScript's handling of truthiness and falsiness. In JavaScript, the following values are considered "false": 'false', '0', '-0', '', 'null', 'undefined', 'NaN' and 'document.all'.

Therefore, if an expression is evaluated as "false", instead of returning a boolean 'false' as in previous versions of JavaScript, modern implementations return the actual evaluated expression.

This behavior explains why the expressions provided in the question result in objects being returned rather than strict boolean values. If either 'obj.fn()' or 'obj._' is defined, it will return the result of that expression, as they are not among the values considered "false".

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