I think I already pointed you once to the syntax Thierry hints at ;-)
Even then, having variable item.prCtr1 .. item.prCtr6 in an object smells like repeating values of a record, with all the arguments of data normalizition speaking against it - are you certain that those profit centers would not be better represented in a list-like structure instead of properties with number mangling in the property name ? In Javascript probably easiest as a stack or queue, which could be expressed as a collection/array, while linked lists seem a better fit for languages where you handle memory (pointers) yourself

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>https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in
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>I am writing a function for checking profit centers. An item can have 6 profit centers. The values are saved as item.prCtr1, item.prCtr2, etc.
>I want to make sure that if they are specified (e.g. not 0/null), then they are all different.
>So, I am going to write like this
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>

>if (item.prCtr1!=0 && item.prCtr1 in new Array(item.prCtr2, item.prCtr3, item.prCtr4, item.prCtr5, item.prCtr6) )

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>The problem here that according to that reference, it will also compare with the array's index and so I may get false positives.
>Do you see a way to write the above code in a simple manner? Or I'd rather write 5 OR checks for all 6 of them?
>What do you think?