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General Tech QA/Testing 2 years ago
Posted on 16 Aug 2022, this text provides information on QA/Testing related to General Tech. Please note that while accuracy is prioritized, the data presented might not be entirely correct or up-to-date. This information is offered for general knowledge and informational purposes only, and should not be considered as a substitute for professional advice.
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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;
Coerces oObject to boolean. If it was falsey (e.g. 0, null, undefined, etc.), it will be false, otherwise, true.
oObject
null
undefined
false
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":
let isIE8 = false; 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
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