undefined - Why is there an isNaN() function in JavaScript but no isUndefined()? -
Why is a isNaN () function in javascript whilst isUndefined () This should be written as:
typeof (...)! = "Undefined" Is there an issue that I do not see?
In my opinion this is actually ugly just isUndefined (testValue) .
Usage case var === undefined works almost everywhere, Except for those cases, where either undefined is assigned to a value, or var is undefined.
Due to such a ceremony can not be present, it is clear from the latter case. If var is undefined, then it is assumed that calling the function isUndefined (var) will result in ReferenceError . Although the introduction of a new keyword, e.g. Asunderfinder Verge can solve this problem.
But despite being valid, both of the above cases are poor use of Javascript, which is why I believe that such a keyword does not exist.
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