JavaScript: multiple array conditions in if statement

Question

I'm pretty new here but i'm posting this cause i haven't found a single answer on the internet to this question.

How can I use multiple arrays as conditions to an if statement. the reason i would need this is simply for creating a 2D game. But i'm learning that even a simple 2D game has tons of variables because of all the objects involved. But here is a simple example for what I've started with.

var a = 27;
var test = 0;

if(a in {18:1, 27:1, 36:1}) {
    test = 1;
}

This tests an array of variables against one variable. I've found that this returns true but this is only half the battle.

The only place I've found any close reference to this is here.

How to shorten my conditional statements

Now the hard part is getting two arrays as conditions instead of just a variable and an array. So basically i need this idea made shorter.

var a = 27;
var b = 27;  
var c = 50;
var test = 0;

if(a in {18:1, 27:1, 36:1} || b in {18:1, 27:1, 36:1} || c in {18:1, 27:1, 36:1}) {  
    test = 1;
}

even though i'm a noob my bible is the hacker's standard:P. Which basically means i think that when i'm creating something with the process of doing something over and over without very good reason "IT IS THE DEVIL"(kudos to whoever got the references). So let me explain this again but very specific so there's no confusion. Say i create a lot of NPC(non player character) and i want a system that can detect if the individual NPC has been in contact by lets say a projectile. i want that individual to vanish and give a point to a score board. well creating functions for such characters requires a LOT of if statements. So ideally i want an if statement that somehow uses 2 or more arrays for it's conditions but look almost as short as using two variables.

maybe something that looks like this.

var test = 0;
var a = [5,6,8];
var b = [10,30,8];

if(a in b){
    test = 1;
}

NOTE: I've actually already tried this but it only took the index of b and not the numbers inside. I believe this topic deserves attention unless there's already someone out there that posted a solution(in which case it NEEDS to be advertised).

EDIT: After a long while i've come to realize that the proper(more efficient and readable) solution is to use both OOP and game engine design. I was just too young to understand how to work with data. So to anyone who see's this wondering the same thing should simply try to more thoroughly study array and class logic. In honesty javascript is NOT the place to learn this. I recommending taking a trip to processing.org. and learning the ways of using classes. if Your having trouble there you can try openFrameworks and learn OOP in c++. But the biggest part is understanding proper array mechanics. The OOP just makes it easier.

Answer 1

var test = false;
var a = [5, 6, 8];
var b = { 10:1, 30:1, 8:1 };
for (var i = 0; i < a.length; i++) {
    if (a[i] in b) {
        test = true;
        break;
    }
}

If you're using a library like jQuery or Underscore.js, they have convenience functions like $.any() that can be used to replace the loop. You can also use the built-in Array#some method, but it's not compatible with IE8. Ex:

return a.some(function(x) {
    return x in b;
});