JavaScript two-dimensional array bracket meaning

JavaScript is a general-purpose, efficient programming language that supports a variety of data types and data structures. Among them, two-dimensional array is a very commonly used data structure, which can be used to store two-dimensional data, such as matrices, chessboards, etc. When using two-dimensional arrays, you often see some brackets. What do these brackets mean? Next, let’s discuss the meaning of JavaScript two-dimensional array brackets.

First, let’s take a look at how to define a two-dimensional array in JavaScript. The method of defining a two-dimensional array is very simple. You only need to nest another array in the array. The example is as follows:

var arr = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
];

A two-dimensional array with 3 rows and 3 columns is defined here. Each row is A one-dimensional array of length 3. We can access the elements in the two-dimensional array through the index of the array, such as accessing the elements in the second row and third column (i.e. the number 6):

console.log(arr[1][2]); // 输出6

In the above code, arr[1] means getting The second one-dimensional array in the two-dimensional array, and arr1 means getting the third element in this one-dimensional array.

Back to our question, what do those square brackets mean? In fact, in JavaScript, square brackets are used to represent array indexes. For a one-dimensional array, it only has a set of square brackets, which means to get the value of a certain element in the array, for example:

var arr = [1, 2, 3];
console.log(arr[1]); // 输出2

where arr[1] means to get the second element in the array, that is The value of the number 2.

For a two-dimensional array, it requires two sets of square brackets. The first set of square brackets is used to indicate obtaining a one-dimensional array in a two-dimensional array, and the second set of square brackets is used to indicate obtaining an element in the one-dimensional array. For example:

var arr = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
];
console.log(arr[1][2]); // 输出6

The arr1 here means to get the second one-dimensional array in the two-dimensional array, and then get the third element in this array, which is the value of the number 6.

It should be noted that square brackets in two-dimensional arrays can be nested. For example, we can define a three-dimensional array:

var arr = [
  [
    [1, 2],
    [3, 4]
  ],
  [
    [5, 6],
    [7, 8]
  ]
];
console.log(arr[1][0][1]); // 输出6

Here arr1[1] means to obtain the second two-dimensional array in the three-dimensional array, and then obtain the first one-dimensional array in this two-dimensional array, Finally, get the second element in this one-dimensional array, which is the value of the number 6.

To sum up, the square brackets in JavaScript two-dimensional arrays are used to indicate the index of the array. The first set of square brackets indicates obtaining a one-dimensional array in the two-dimensional array, and the second set of square brackets indicates obtaining a one-dimensional array in the two-dimensional array. The brackets indicate obtaining an element in this one-dimensional array. It should be noted that square brackets in two-dimensional arrays can be nested.

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