Welcome! I don’t want to spend too much time in the introduction this time, but today I will (hopefully) teach you and show you technically six array methods that you probably didn’t know!

Table Of Contents

  1. concat()
  2. some()
  3. entries()
  4. find() and findIndex()
  5. copyWithin()
  6. Conclusion


The concat array method returns a new array populated with two or more arrays merged. It does not alter any existing arrays, but rather creates a new one.


const foo = [1, 2, 3';
const bar = [4, 5, 6];

const foobar = foo.concat(bar);
// expected return: [1, 2, 3, 4, 5, 6]


This array method tests whether or not at least one element in the array passes a test. It returns true if it finds at least one element that returns true in the provided function (callback function), else it returns false.


const foobar = [7, 13, 23];

const isValid = (elm) => elm > 13

// expected return: true


The entries method returns a new Array iterator object that contains the key/value of each index of an array.


const foobar = ['a', 'b', 'c']
const iterator = foobar.entries()

// expected return: Array [0, "a"]

// expected return: Array [1, "b"]

// expected return: Array [2, "c"]

find() and findIndex()

Returns the first element in an array that passes a test in the provided arrow function. If no element matches, then it returns undefined.


const foobar = [10, 15, 20, 25, 30]

const test = foobar.find(elm => elm > 18)

// expected return: 20

findIndex is very similar, but instead only returns the index, and if no element matches the test provided, then returns -1. The example above is expected to return 3.


I’m not even gonna lie, I still find this one a bit confusing because of the syntax, but might be useful in some situations. This method copies array elements to another position of the same array.

syntax: array.copyWithin(target, start, end)

Note that the end and start parameters are not required and if not specified, will use the first or last elements of the array.


const foobar = ["a", "b", "c"]
console.log(foobar.copyWithin(2, 0, 2))
// expected return: Array ["a", "b", "a"]


Did you know all of these? Because to be honest, I didn’t either until I finished writing this article hahaha. But now that I do, I can think of plenty of situations where these might come in useful.

I appreciate you spending your time reading this post, if you’d like to read more here you go:

🔥 STOP! Use this instead of create-react-app!

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