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I saw some code that seems to use an operator I don't recognize, in the form of two exclamation points, like so: !!. Can someone please tell me what this operator does?
The context in which I saw this was,
this.vertical = vertical !== undefined ? !!vertical : this.vertical; 
922
What Does NOT Operator Mean? In Boolean algebra, the NOT operator is a Boolean operator that returns TRUE or 1 when the operand is FALSE or 0, and returns FALSE or 0 when the operand is TRUE or 1. Essentially, the operator reverses the logical value associated with the expression on which it operates.
The inequality operator ( != ) checks whether its two operands are not equal, returning a Boolean result. Unlike the strict inequality operator, it attempts to convert and compare operands that are of different types.
symbol is used to indicate whether the expression defined is false or not. For example, !( 5==4) would return true , since 5 is not equal to 4. The equivalent in English would be not .
Converts Object to boolean. If it was falsey (e.g. 0, null, undefined, etc.), it will be false, otherwise, true.
!oObject // inverted boolean !!oObject // non inverted boolean so true boolean representation So !! is not an operator, it's just the ! operator twice.
Real World Example "Test IE version":
const isIE8 = !! navigator.userAgent.match(/MSIE 8.0/); console.log(isIE8); // returns true or false If you ⇒
console.log(navigator.userAgent.match(/MSIE 8.0/)); // returns either an Array or null But if you ⇒
console.log(!!navigator.userAgent.match(/MSIE 8.0/)); // returns either true or false If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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