Access Multi-Dimensional Arrays With Indexes:

One way to think of a multi-dimensional array, is as an array of arrays. When you use brackets to access your array, the first set of brackets refers to the entries in the outer-most (the first level) array, and each additional pair of brackets refers to the next level of entries inside.

Example:

const arr = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
  [[10, 11, 12], 13, 14]
];

arr[3];
arr[3][0];
arr[3][0][1];

arr[3] is [[10, 11, 12], 13, 14], arr[3][0] is [10, 11, 12], and arr[3][0][1] is 11.

Note: There shouldn't be any spaces between the array name and the square brackets, like array [0][0] and even this array [0] [0] is not allowed. Although JavaScript is able to process this correctly, this may confuse other programmers reading your code.

Manipulate Arrays With push():

An easy way to append data to the end of an array is via the push() function.

.push() takes one or more parameters and "pushes" them onto the end of the array.

Examples:

const arr1 = [1, 2, 3];
arr1.push(4);

const arr2 = ["Stimpson", "J", "cat"];
arr2.push(["happy", "joy"]);

arr1 now has the value [1, 2, 3, 4] and arr2 has the value ["Stimpson", "J", "cat", ["happy", "joy"]].

Manipulate Arrays With pop():

Another way to change the data in an array is with the .pop() function.

.pop() is used to pop a value off of the end of an array. We can store this popped off value by assigning it to a variable. In other words, .pop() removes the last element from an array and returns that element.

Any type of entry can be popped off of an array - numbers, strings, even nested arrays.

const threeArr = [1, 4, 6];
const oneDown = threeArr.pop();
console.log(oneDown);
console.log(threeArr);

The first console.log will display the value 6, and the second will display the value [1, 4].

Manipulate Arrays With shift():

pop() always removes the last element of an array. What if you want to remove the first?

That's where .shift() comes in. It works just like .pop(), except it removes the first element instead of the last.

Example:

const ourArray = ["Stimpson", "J", ["cat"]];
const removedFromOurArray = ourArray.shift();

removedFromOurArray would have a value of the string Stimpson, and ourArray would have ["J", ["cat"]].

Manipulate Arrays With unshift():

Not only can you shift elements off of the beginning of an array, you can also unshift elements to the beginning of an array i.e. add elements in front of the array.

.unshift() works exactly like .push(), but instead of adding the element at the end of the array, unshift() adds the element at the beginning of the array.

Example:

const ourArray = ["Stimpson", "J", "cat"];
ourArray.shift();
ourArray.unshift("Happy");

After the shift, ourArray would have the value ["J", "cat"]. After the unshift, ourArray would have the value ["Happy", "J", "cat"].