Be careful when using instanceof

If you intend to throw an error if an object is not an instanof a specific object, be careful of this mistake that's easy to make.


if( !someVar instanceof SomeObject){  //WRONG!
throw new Error("....");

 If someVar is null or undefined then your error will not be thrown.


This is better:


if( !(someVar instanceof SomeObject)){  
throw new Error("....");






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