What do you want from your Array?

You need to select at least one option.

None of the methods provided here mutate the original array.

These methods aren't included here:

Array.prototype.map()

If you're looking for another array with all elements of the original array being modified by some function, then you should use the .map() method.

MDN 
// pass a function to map
const result = ['Cat', 'Griffin', 'Wolf'].map(x => 'School of ' + x);
console.log(result);
// Output: Array ['School of Cat', 'School of Griffin', 'School of Wolf']

Array.prototype.filter()

If you're looking for all elements which match a condition, then you should use the .filter() method.

MDN 
// pass a function to filter
const words = ['witcher', 'hunter', 'king', 'guard'];
const allMatches = words.filter(x => x.length < 6);
console.log(allMatches);
// Output: Array ['king', 'guard']

Array.prototype.concat()

If you're looking to merge multiple arrays without changing the original arrays, then you should use the .concat() method.

MDN 
const heroes = ['Geralt', 'Vesemir'].concat(['Ciri', 'Yennefer']);
console.log(heroes);
// Output: Array ['Geralt', 'Vesemir', 'Ciri', 'Yennefer']

Array.prototype.find()

If you're looking for the first element which matches a condition from a given array, then you should use the .find() method.

MDN 
// pass a function to find
const words = ['witcher', 'hunter', 'king', 'guard'];
const firstMatch = words.find(x => x.length < 6);
console.log(firstMatch);
// Output: String 'king'

Array.prototype.findIndex()

If you're looking for the index of the first element which matches a condition from a given array, then you should use the .findIndex() method.

MDN 
// pass a function to findIndex
const words = ['witcher', 'hunter', 'king', 'guard'];
const firstMatch = words.findIndex(x => x.length < 6);
console.log(firstMatch);
// Output: 2

Array.prototype.join()

If you're looking to combine all array elements (with something separating them or not), then you should use the .join() method.

MDN 
const result = ['Toss', 'a', 'coin'].join(' '));
console.log(result);
// Output: String 'Toss a coin'

Array.prototype.every()

If you're checking whether every element from a given array matches a certain condition, then you should use the .every() method.

MDN 
// pass a function to every
const words = ['witcher', 'hunter', 'king', 'guard'];
const lessThan10 = words.every(x => x.length < 10);
console.log(lessThan10);
// Output: true

const greaterThan10 = words.every(x => x.length > 10);
console.log(greaterThan10);
// Output: false

Array.prototype.some()

If you're checking whether at least one element from a given array matches a certain condition, then you should use the .some() method.

MDN 
// pass a function to some
const words = ['witcher', 'hunter', 'king', 'guard'];
const anyLessThan6 = words.some(x => x.length < 6);
console.log(anyLessThan6);
// Output: true

const anyGreaterThan10 = words.some(x => x.length > 10);
console.log(anyGreaterThan10);
// Output: false

Array.prototype.includes()

If you're checking whether a certain element exists in the given array, then you should use the .includes() method.

MDN 
const witchers = ['Geralt', 'Ciri', 'Vesemir'];

const isCiriAWitcher = witchers.includes('Ciri');
console.log(isCiriAWitcher);
// Output: true

const isYenneferAWitcher = words.includes('Yennefer');
console.log(isYenneferAWitcher);
// Output: false

Array.prototype.forEach()

If you're looking to perform some operation(s) on every element from a given array, then you should use the .forEach() method.

MDN 
['Geralt', 'Vesemir', 'Ciri'].forEach(x => {
    console.log(x + ', the Witcher');
});

// Output:
// Geralt, the Witcher
// Vesemi, the Witcher
// Ciri, the Witcher

Array.prototype.reduce()

If you're looking to calculate a single value from array elements, then you should use the .reduce() method.

MDN 
// This example is for numbers, but it works for strings as well.
const numbers = [1, 2, 3, 4];
const reducerFunction = (inventory, loot) => inventory + loot;

const saddleBag = numbers.reduce(reducerFunction);
console.log(saddleBag); // Output: 10

const existingLoot = 50;
const stash = numbers.reduce(reducerFunction, existingLoot);
console.log(stash); // Output: 60