or を使わない書き方

var val='bbb'
alert(val=='aaa' || val=='bbb' || val=='ccc')//true
↓
var val='bbb'
alert(/aaa|bbb|ccc/i.test(val))//true

おまけ
プロパティ名のオブジェクト内の有無を調べる時は in を使う

var name='bbb'
var vals={
	aaa:false,
	bbb:false,
	ccc:false
}
alert(vals[name]); //false
alert(vals.hasOwnProperty(name)); //true
alert(name in vals); //true

var vals={
	aaa:undefined,
	bbb:undefined,
	ccc:undefined
}
alert(vals[name]); //undefined
alert(typeof vals[name]!='undefined'); //false
alert(vals.hasOwnProperty(name)); //true
alert(name in vals); //true

var f=function(){}
f.prototype={
	aaa:false,
	bbb:false,
	ccc:false
}
var vals=new f;
alert(vals[name]); //false
alert(typeof vals[name]!='undefined'); //true
alert(vals.hasOwnProperty(name)); //false
alert(name in vals); //true