Since nobody has added the obvious solution yet which works fine for two comparisons, I'll offer it:

if (foobar == foo || foobar == bar) {
     //do something
}

And, if you have lots of values, then I'd suggest making a Set as this makes very clean and simple comparison code and it's fast at runtime:

// pre-construct the Set
var tSet = new Set([foo, bar, test1, test2, test3]);

// test the Set at runtime
if (tSet.has(foobar)) {
    // do something
}

For pre-ES6, you can get a Set polyfill of which there are many. One is described in this other answer.

A quick overview of new JavaScript features in ES2015, ES2016, ES2017 and beyond.