Working With Nested Arrays in JavaScript

Detailed explanation of JavaScript array

JavaScript array is a collection of data stored in list form. Arrays are accessed using indexes, which means that each array item can be accessed through an integer index starting from 0.

For example, a simple array looks like this:

let myArray = [1, 2, 3, 4, 5];

In this example, the first element of the array is indexed to 0, the second element is indexed to 1, and so on.

Arrays are often used to store collections of data that require quick and easy access. For example, if you have a group of users in your application, you can store them in an array and access them through an index.

let users = ["John", "Jane", "Jack"];
console.log(users[0]); // 输出： "John"

Arrays can store various types of values, including strings, numbers, and objects. It is completely valid to store different types of values ​​in the same array.

const varied = [null, undefined, NaN, "string", 12345, {name: "Sam"}];

You can also store (or nest) an array in another array. This will create a so-called two-dimensional array.

JavaScript nested arrays

A two-dimensional array (also known as an array of arrays) is just an array containing one or more subarrays. These child arrays are called nested in the parent array.

const arrayOfArr = [
  ['value 1', 'value 2'],
  ['value 3', 'value 4'],
  ['value 5', 'value 6']
];

Nested arrays can be used to group related elements. For example, let's look at the following two-dimensional array:

const animalPairs = [
  // 母的和公的
  ['doe', 'buck'],
  ['ewe', 'ram'],
  ['peahen', 'peacock'],
  ['cow', 'bull'],
];

Here, we pair the female and male names of the same animal into each nested array. The female is on the left and the male is on the right.

To access the first element, you can use index 0 as shown below:

animalPairs[0]

Print results in the console:

console.log(animalPairs[0]) // ['doe', 'buck'],

Now, to access the values ​​in the nested array, you must add a second parentheses that contain the index of the values ​​to be accessed. For example, suppose you want to get the female name from the first array. Since you know that females are always in front, you just need:

• Use [0] to get the first element in this nested array (in this case the female name):

animalPairs[0][0]

The output is as follows:

console.log(animalPairs[0][0]) // 'doe'

If you want to get the second element in the first nested array:

animalPairs[0][1] // 'buck'

In this case, there are only two elements in each nested array, so our index terminates at [ ] and returns the nested array, while the second unshift() method:

const animalPairs = [
  // 将在此处插入母鸡和公鸡
  ['doe', 'buck'],
  ['ewe', 'ram'],
  ['peahen', 'peacock'],
  ['cow', 'bull'],
];
animalPairs.unshift(['hen', 'rooster']);

To insert an array at the end of the parent, pass the array to the shift() method on the parent array:

const animalPairs = [
  ['doe', 'buck'], // 删除此项
  ['ewe', 'ram'],
  ['peahen', 'peacock'],
  ['cow', 'bull'],
];
animalPairs.shift();

Finally, to delete the last array, do id, username, etc.

However, understanding how to access and manipulate data in nested arrays helps you better understand the language. It also helps you master the syntax for traversing complex array structures in JavaScript.

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