You can also use Array.indexOf:
var days = ["monday",
"tuesday",
"wednesday",
"thursday",
"friday",
"saturday",
"sunday"];
function isInArray(days, day) {
return days.indexOf(day.toLowerCase()) > -1;
}
isInArray(days, "Sunday");
isInArray(days, "sunday");
isInArray(days, "sUnDaY");
isInArray(days, "Anyday");
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