javascript array usage

JavaScript is a scripting language widely used in web front-end development. It allows developers to achieve rich interactive effects in web pages through its concise syntax, flexibility and ease of use. Among them, JavaScript array is a very useful data structure, which can store multiple data and perform various operations. This article takes an in-depth look at the usage of JavaScript arrays and provides some practical tips for beginners and intermediate developers.

What is a JavaScript array

First, let us understand the concept of a JavaScript array. Simply put, an array is a data structure consisting of several elements of any data type, arranged in a certain order, and referenced by a subscript. In an array, each element has its own position, called a subscript or index, which increases from 0.

The following is a simple JavaScript array example, which represents an array containing 5 integers:

var myArray = [10, 20, 30, 40, 50];

In this array:

• 10 is the first element, its subscript is 0;
• 20 is the second element, its subscript is 1;
• 30 is the third element, its subscript is 2;
• 40 is the fourth element, its subscript is 3;
• 50 is the fifth element, and its subscript is 4;

When we need to access an element in the array, we can use square brackets[ ] Add the subscript of the element to reference it, such as:

console.log(myArray[2]); // 30

This line of code will output the element with subscript 2 in the array, that is, 30.

Common operations on JavaScript arrays

Next, we will introduce some of the most commonly used operations on JavaScript arrays one by one:

Creating arrays

JavaScript arrays can be Created in two ways. The first method is to use square brackets [] to get an empty array, and then add elements to it one by one:

var myArray = [];
myArray[0] = "apple";
myArray[1] = "orange";
myArray[2] = "banana";

The second method is to directly put the elements in square brackets, in Declare the array in the statement:

var myArray = ["apple", "orange", "banana"];

Access the array elements

You can use square brackets [] plus the subscript of the element to access the elements in the array, or you can use a loop Access all elements at once:

var myArray = [10, 20, 30];
console.log(myArray[0]); // 10

for (var i = 0; i < myArray.length; i++) {
  console.log(myArray[i]);
}

This code will output all elements in the array, that is:

10
20
30

Add array elements

To add an element at the end of the array, you can use push() method; add an element at the beginning of the array, you can use unshift() method:

var myArray = [10, 20, 30];
myArray.push(40); // 添加元素 40 到数组末尾
myArray.unshift(0); // 添加元素 0 到数组开头
console.log(myArray); // [0, 10, 20, 30, 40]

Delete the array element

At the end of the array To delete an element, you can use the pop() method; to delete an element at the beginning of the array, you can use the shift() method; to delete an element at any position, you can use splice( ) Method:

var myArray = [0, 10, 20, 30, 40];
myArray.pop(); // 删除最后一个元素
myArray.shift(); // 删除第一个元素
myArray.splice(1, 2); // 删除第 2~3 个元素
console.log(myArray); // [20, 30]

Among them, the first parameter of the splice() method is the starting position of deletion, and the second parameter is the number of deletions.

Find elements

You can use the indexOf() method to find whether an array contains an element. This method will return the subscript of the first occurrence of the element, or -1 (if not found):

var myArray = [10, 20, 30, 20, 40];
console.log(myArray.indexOf(20)); // 1
console.log(myArray.indexOf(50)); // -1

Array sorting

You can use the sort() method to sort the elements in the array, default It is arranged in string order. You can pass a comparison function to customize the sorting rules:

var myArray = [40, 10, 30, 20, 50];
myArray.sort();
console.log(myArray); // [10, 20, 30, 40, 50]

myArray.sort(function(a, b) {
  return a - b;
});
console.log(myArray); // [10, 20, 30, 40, 50]

Array reverse

You can use the reverse() method to change the elements in the array Flip:

var myArray = [10, 20, 30, 40, 50];
myArray.reverse();
console.log(myArray); // [50, 40, 30, 20, 10]

Other uses of JavaScript arrays

In addition to the common operations introduced above, there are many other uses of JavaScript arrays.

Array splicing

You can use the concat() method to splice multiple arrays into one array:

var array1 = [10, 20];
var array2 = [30, 40];
var result = array1.concat(array2);
console.log(result); // [10, 20, 30, 40]

Array splitting

You can use the slice() method to extract part of the array and generate a new array:

var myArray = [10, 20, 30, 40, 50];
console.log(myArray.slice(1, 4)); // [20, 30, 40]

Among them, the first parameter of the slice() method is The starting point subscript, the second parameter is the ending point subscript, excluding the element pointed to by the ending point subscript.

Array mapping

You can use the map() method to perform certain processing on each element in the array and return a new array:

var myArray = [10, 20, 30];
var result = myArray.map(function(item) {
  return item * 2; // 将每个元素乘以 2
});
console.log(result); // [20, 40, 60]

Array filtering

You can use the filter() method to filter elements that meet the conditions in the array and return a new array:

var myArray = [10, 20, 30];
var result = myArray.filter(function(item) {
  return item > 15; // 筛选大于 15 的元素
});
console.log(result); // [20, 30]

Array iteration

You can use the forEach() method to perform certain operations on each element in the array without returning any value:

var myArray = [10, 20, 30];
myArray.forEach(function(item) {
  console.log(item); // 输出每个元素
});

Array length

You can use length Attribute to get the length of the array:

var myArray = [10, 20, 30];
console.log(myArray.length); // 3

Summary

Through the introduction of this article, we can understand the basic usage and common operations of JavaScript arrays, so that we can be more flexible and flexible during the development process. Use arrays efficiently. Of course, the functions of JavaScript arrays are far more than this. For advanced developers, there are more advanced techniques and applications. We hope that readers can continue to explore and discover its powerful capabilities in the process of learning and using JavaScript arrays, thereby creating more interesting and practical web page interaction effects.

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