What does !! in js mean?

The !! operator in JS: used to convert a value to a Boolean value. Operation: Perform logical NOT operation on the value. Then perform a logical NOT operation on the result. Result: true: when the value is not false, not the empty string, not null, not undefined. False: When the value is true, empty string, null, undefined. Purpose: Convert any value to a Boolean value. Forces an explicit conversion to a boolean value. Eliminate uncertain values.

!! in JS

In JavaScript, the "!!" operator is a logical negation ( NOT) operator, used to convert a value to a Boolean value. Its function is double negation, that is, after performing a logical NOT operation on the value, perform a logical NOT operation again.

How to use

Syntax:

<code>!!<value></code>

where can be any JavaScript value.

Operation result

• If is true (true), then !! is true (true).
• If is false, then !! is false.
• If is an empty string, null, or undefined, then !! is false.

The purpose of double negation

Double negation operator!! Mainly used for the following purposes:

• Convert any value to a Boolean value: It can convert any value (number, string, object, etc.) into a Boolean value, making it suitable for Boolean operations.
• Force Boolean value: It can force the true value (true) or false value (false) to be explicitly converted to a Boolean value.
• Eliminate undefined values: It can eliminate the concept of "undefined values" in JavaScript, because !! will always return true or false.

Code Example

<code>console.log(!!true); // true
console.log(!!false); // false
console.log(!!0); // false
console.log(!!1); // true
console.log(!!''); // false
console.log(!!'abc'); // true</code>

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