if-indexOf.js

var days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Saturday", "Sunday"];

if( days.indexOf("Wednesday") > -1 ){
  console.log("contains Wednesday!");
}

// same as
var containsWednesday = days.some(function(element){
  return element === "Wednesday";
});
if( containsWednesday ){
  console.log("contains Wednesday!");
}

// same as
if( days.some(function(element){return element === "Wednesday"}) ){
  console.log("contains Wednesday!");
}