Checking Whether an Array Contains an Item

Often you will need to check whether an array contains a certain item. You can do this by using the indexOf() method. If the code does not find the item in the list, it returns a -1. The following function writes a message to the console if an item is in the week array:

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function message(day){
  var week = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"];
  if (week.indexOf(day) != -1){
    console.log("Happy " + day);
  }
}