Concise way to compare multiple element values in Javascript/jQuery?

You can take a functional approach, and create a simple comparison function generator:

function eq(val) {
    return function(x) {
        return x === val
    }
}

And then use .every for the &&:

if ([a,b,c].every(eq(1))) {
    // all were equal
}

Or use .some for the ||:

if ([a,b,c].some(eq(1))) {
    // at least one was equal
}

You could also create a function that receives the result of a condition and a function to invoke when the condition was true:

function when(cond, fn) {
    if (cond)
        fn.call.apply(fn, [].slice.call(arguments, 2))
}

And encapsulate your if body into a function...

function doIt(arg1, arg2) {
    console.log("doing it!")
    console.log(this, arg1, arg2)
}

Then use it like this:

when([a,b,c].every(eq(1)), doIt, null, "foo", "bar")

The third argument to when sets the this value of the callback, and subsequent arguments are passed as arguments to the callback.

Depending on how much you want to invest, that would be a possible solution:

var slice=Function.call.bind([].slice)

var checkCondition=function(condition){ 
    return function(){
        return slice(arguments).reduce(function(o,n){
            return o && o == condition(n);
        },true);
    }
}

greater5=checkCondition(function(x){ return x>5; });

console.log(greater5(4,7));

If you only have one or two times in your code where you have to check multiple variables it would be absolutely overkill. But if you have multiple places with varying arguments, it might help.

You could easily define new checks by definition of another function and add as many variables as you want.