The !! operator reassures the lint tool that what you wrote is what you meant: do this operation, then take the truth value of the result. A third use is to produce logical XOR and logical XNOR.

Understanding the Context

What does the !! (double exclamation mark) operator do in JavaScript ... <> operator means not equal to in MS SQL. It compares two expressions (a comparison operator).

Key Insights

When you compare nonnull expressions, the result is TRUE if the left operand is not equal to the right operand; otherwise, the result is FALSE. If either or both operands are NULL, see the topic SET ANSI_NULLS (Transact-SQL). See here : Not Equal To Also check : 1) Not equal <> != operator on NULL 2 ... 1 That is the modulo operator, which finds the remainder of division of one number by another. So in this case a will be the remainder of b divided by c.

Final Thoughts

The strict equality operator (===) behaves identically to the abstract equality operator (==) except no type conversion is done, and the types must be the same to be considered equal. Reference: JavaScript Tutorial: Comparison Operators The == operator will compare for equality after doing any necessary type conversions. The === operator will not do the conversion, so if two values are not the ... Which equals operator (== vs ===) should be used in JavaScript ... What is the ?: (question mark and colon operator aka. conditional or "ternary") operator and how can I use it?

The & operator does "run these 3 functions, and if one of them returns false, execute the else block", while the | does "only run the else block if none return false" - can be useful, but as said, often it's a design smell. There is a Second use of the | and & operator though: Bitwise Operations.