Can someone explain this ‘double negative’ trick? [duplicate]

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A logical NOT operator ! converts a value to a boolean that is the opposite of its logical value.

The second ! converts the previous boolean result back to the boolean representation of its original logical value.

From these docs for the Logical NOT operator:

Returns false if its single operand can be converted to true; otherwise, returns true.

So if getContext gives you a “falsey” value, the !! will make it return the boolean value false. Otherwise it will return true.

The “falsey” values are:

  • false
  • NaN
  • undefined
  • null
  • "" (empty string)
  • 0

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