Concise way to compare against multiple values

You could use this...

if (["something", "nothing", "anything", "everything"].includes(a)) {
   alert('Who cares?');
}

If you're stuck with older browser support...

if (["something", "nothing", "anything", "everything"].indexOf(a) > -1) {
   alert('Who cares?');
}

You also tagged it jQuery, so if you need to support older browsers without Array.prototype.indexOf(), you could use $.inArray().

You can put the options in array and use jQuery $.inArray() or javascrpt indexOf() to search array

Pure javascript  

Live Demo

var a = 'anything';
arr = ['something', 'nothing', 'anything', 'everything'];
if(arr.indexOf(a) != -1)
    alert("condition met");    
else
    alert("condition not met");    

With jQuery

Live Demo

var a = 'jesus';
arr = ['something', 'nothing', 'anything', 'everything'];

if($.inArray(a, arr) != -1) // With jQuery
    alert("condition met");    
else
    alert("condition not met");    

With ES7 you are able to use Array.prototype.includes and even shorter notation than indexOf, which is already implemented in every modern browser.

Here is the example usage:

if (['hero', 'anything', 'everything'].includes(me)) {
    alert('Who cares?');
}

And the polyfill from Mozilla.

With a regex:

if (/^(something|nothing|anything|everything)$/.exec('jesus')) alert('Who cares?');​

Or the opposite:

/^(something|nothing|anything|everything)$/.exec('jesus')||alert('Who cares?');​

[Update] Even shorter ;-)

if (/^(some|no|any|every)thing$/.exec('jesus')) alert('Who cares?');​