Understanding JavaScript's Quirks: Why "0" Is False but Not False in if Statements

In JavaScript, the evaluation of a value in a logical context—such as in if statements or Boolean comparisons—can produce unexpected results. This behavior is due to JavaScript's type coercion mechanism.

JavaScript loosely types its values, and when a string or number value is used in a logical context, it undergoes type coercion to convert it to a boolean value. In this conversion, non-empty strings and non-zero numbers evaluate to true, while empty strings and zero numbers evaluate to false.

Therefore, when you compare "0" to false using == or ===, it returns true because type coercion converts both "0" (a non-empty string) and false (a zero-like value) to true.

However, when using an if statement, "0" alone evaluates to true. This is because if statements internally use a coerced boolean value, which returns true for non-empty strings.

To avoid any ambiguity, it is recommended to use the strict equality operator === when comparing primitive values, as it performs a comparison without type coercion. This ensures that "0" is correctly evaluated as false when necessary.

Refer to the attached tables for a concise representation of JavaScript's truthy/falsy behavior for various data types. Remember, for true equality comparisons, always opt for ===.