Is it possible to check for both null and undefined in javascript?
if(_var == null || _var == undefined) {
}
In JavaScript (pre ECMAScript 5), undefined
is not a constant, but a global variable, and therefore it is possible to change its value. Therefore it would be more reliable to use the typeof
operator to check for undefined
:
if (typeof _var === 'undefined') { }
In addition your expression would return a ReferenceError if the variable _var
is not declared. However you would still be able to test it with the typeof
operator as shown above.
Therefore, you may prefer to use the following:
if (typeof _var === 'undefined' || _var === null) { }
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