What is it

Returns boolean indicating whether an array includes a certain value among its entries

const items = [1,2,3,4,5];
const includesTwo = items.includes(7);

console.log(includesTwo); // false

const array1 = ["element1", "element2"];
array1.includes("element2"); // true

Additional Examples

const pets = ['cat', 'dog', 'bat'];
console.log(pets.includes('cat')); // true
console.log(pets.includes('at')); // false

// additional examples
[1, 2, 3].includes(2)         // true
[1, 2, 3].includes(4)         // false
[1, 2, 3].includes(3, 3)      // false
[1, 2, 3].includes(3, -1)     // true
[1, 2, NaN].includes(NaN)     // true
["1", "2", "3"].includes(3)   // false

Example: check if guest is on the guest list

const guestList = ["guest1", "guest2"];

let guestName = prompt("What is your name?");

if (guestList.includes(guestName)) { 
  alert("Welcome"); 
}
else { 
  alert("Sorry you are not on the list"); 
}