Summary of 20 common JavaScript array operations

ArrayObject in JavaScript, like arrays in other programming languages, is a collection of data. In JavaScript, the data inside an array can be of different types and has methods for performing common operations on arrays.

Declare arrays

There are three different declaration methods

1. Conventional method

const hobbys = new Array()
hobbys[0] = 'Basketball'
hobbys[1] = 'Badminton'
hobbys[2] = 'swimming'
console.log(hobbys)
// [ 'Basketball', 'Badminton', 'swimming' ]

2. Concise method

const hobbys = new Array('Basketball', 'Badminton','swimming')
console.log(hobbys)
// [ 'Basketball', 'Badminton', 'swimming' ]

3. Literal

const hobbys = ['Basketball','Badminton','swimming']
console.log(hobbys)
// [ 'Basketball', 'Badminton', 'swimming' ]

Array object method

1. forEach

forEach() method is used to call each element of the array and pass the element to the callback function. There is no return value, which is essentially equivalent to a for loop that executes the function function on each item. The original array will not be changed.

// currentValue:必需,当前元素 index:可选,当前元素的索引值 arr:可选,当前元素所属的数组对象。
array.forEach(function(currentValue, index, arr))

let array = ['a', 'b', 'c']
let func = (currentValue, index, arr) => {
  currentValue += 's'  
  console.log('currentValue：' + currentValue + ' index：' + index + ' arr：' + arr)
}
array.forEach(func)
console.log(array)

// 控制台输出：
// currentValue：as index：0 arr：a,b,c
// currentValue：bs index：1 arr：a,b,c
// currentValue：cs index：2 arr：a,b,c
// [ 'a', 'b', 'c' ]

2. map

Processes each element of the array through the specified function and returns the processed array.

The map() method returns a new array, and the elements in the array are the values ​​of the original array elements after calling the function. The method processes elements sequentially in the original array element order. The original array will not be changed.

// currentValue:必须,当前元素的值  index:可选,当前元素的索引值 arr:可选,当前元素属于的数组对象
array.map(function(currentValue,index,arr))

let array = [1, 2, 3, 4, 5]
let result = array.map((item) => { 
  return item += 5
})
console.log(array)
console.log(result)
// [ 1, 2, 3, 4, 5 ]
// [ 6, 7, 8, 9, 10 ]

3. concat

The concat() method in JavaScript is used to concatenate two or more arrays and return the result.

// array1, array2, ..., arrayN 必需,该参数可以是具体的值,也可以是数组对象,可以是任意多个
array1.concat(array2,array3,...,arrayN)

const array1 = ['a', 'b', 'c']
const array2 = ['d', 'e', 'f']
const array3 = array1.concat(array2)
console.log(array3)
const array4 = array1.concat('123')
console.log(array4)
// [ 'a', 'b', 'c', 'd', 'e', 'f' ]
// [ 'a', 'b', 'c', '123' ]

4. push

The push() method in Javascript array is used to add one or more elements to the end of the array, and Returns the new length.

let fruits = ["Banana", "Orange", "Apple", "Mango"]
let length = fruits.push("Kiwi")
console.log(fruits)
console.log(length)
// [ 'Banana', 'Orange', 'Apple', 'Mango', 'Kiwi' ]
// 5

5. unshift

The unshift() method adds one or more elements to the beginning of the array and returns the new length.

let fruits = ["Banana", "Orange", "Apple", "Mango"]
let length = fruits.unshift("Lemon", "Pineapple")
console.log(fruits)
console.log(length)
// [ 'Lemon', 'Pineapple', 'Banana', 'Orange', 'Apple', 'Mango' ]
// 6

6. pop

The pop() method is used to delete the last element of the array and return the deleted element.

let sites = ['Google', 'Runoob', 'Taobao', 'Zhihu', 'Baidu']
let result = sites.pop()
console.log(sites)
console.log(result)
// [ 'Google', 'Runoob', 'Taobao', 'Zhihu' ]
// Baidu

7. shift

The shift() method is used to delete the first element of the array and return the value of the first element

let fruits = ["Banana", "Orange", "Apple", "Mango"];
let result = fruits.shift()
console.log(fruits)
console.log(result)
// [ 'Orange', 'Apple', 'Mango' ]
// Banana

8. splice

splice() method is used to add or delete elements in the array and return the deleted element array

// 参数 Values: index: 必需,规定从何处添加/删除元素
// howmany: 可选,规定应该删除多少元素 必须是数字,但可以是 "0"
// item1, ..., itemX 可选,要添加到数组的新元素
array.splice(index,howmany,item1,.....,itemX)

let fruits = ["Banana", "Orange", "Apple", "Mango"]
let result = fruits.splice(1, 2, "Lemon", "Kiwi")
console.log(fruits)
console.log(result)
// [ 'Banana', 'Lemon', 'Kiwi', 'Mango' ]
// [ 'Orange', 'Apple' ]

9 The .slice

slice() method returns selected elements from an existing array. You can also extract a portion of a string and return the extracted portion as a new string. The original array will not be changed.

// start: 可选,规定从何处开始选取 若为负值,表示从原数组中的倒数第几个元素开始提取
// end: 可选,规定从何处结束选取 如果没有指定该参数,那么切分的数组包含从start到数组结束的所有元素
array.slice(start, end)

let fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"]
let result1 = fruits.slice(1, 3)
let result2 = fruits.slice(2)
console.log(fruits)
console.log(result1)
console.log(result2)
// [ 'Banana', 'Orange', 'Lemon', 'Apple', 'Mango' ]
// [ 'Orange', 'Lemon' ]
// [ 'Lemon', 'Apple', 'Mango' ]

10. join

join() method combines all array elements into a string. It behaves like toString(), but you can also specify the delimiter

// separator: 可选,指定要使用的分隔符 如果省略该参数,则使用逗号作为分隔符
array.join(separator)

let fruits = ["Banana", "Orange", "Apple", "Mango"];
let energy1 = fruits.join();
let energy2 = fruits.join('-');
console.log(energy1)
console.log(energy2)
// Banana,Orange,Apple,Mango
// Banana-Orange-Apple-Mango

11. The every

every() method is used to detect whether all elements of the array match Specify the condition (provided through the function).

array.every(function(currentValue,index,arr))

let ages = [32, 33, 16, 40]
let nums = [32, 33, 19, 40]
function checkAdult(age) {
  return age >= 18
}
function checkNums(num) {
  return num >= 18
}
// 16不满足大于18，故结果false
let result1 = ages.every(checkAdult)
// 每一项都满足条件，故结果true
let result2 = nums.every(checkNums)
console.log(result1)
console.log(result2)
// false
// true

12. The filter

filter() method creates a new array. The elements in the new array are checked for all elements in the specified array that meet the conditions. The original array will not be changed.

array.filter(function(currentValue,index,arr), thisValue)

let ages = [32, 33, 16, 40];
function checkAdult(age) {
  return age >= 18;
}
let result = ages.filter(checkAdult)
console.log(result)
// [ 32, 33, 40 ]

13. The indexOf

indexOf() method returns the position where a specified string value first appears in the string. If not found, -1

// searchvalue: 必需。规定需检索的字符串值。
// start: 可选的整数参数。规定在字符串中开始检索的位置。值：0~array.length-1
string.indexOf(searchvalue,start)

let str = "Hello world, welcome to the universe.";
// 输出w所在的下标索引13（空格也算），没有找到会返回-1
let n = str.indexOf("welcome");
console.log(n)
console.log(str[n])
// 13
// w

14. reduce

reduce() method receives a function as an accumulator, each value in the array (from left to right ) begins to reduce and is finally calculated to a value.

array.reduce(function(total, currentValue, currentIndex, arr), initialValue)

let numbers = [2, 3, 5, 6]
function getSum(total, num) {
  return total + num
}
let result = numbers.reduce(getSum, 0)
console.log(result)
// 16

15. reverse

reverse() method is used to reverse the order of elements in the array. Will change the original array and return the array in changed order.

let fruits = ["Banana", "Orange", "Apple", "Mango"]
let resut = fruits.reverse()
console.log(fruits)
console.log(resut)
// [ 'Mango', 'Apple', 'Orange', 'Banana' ]
// [ 'Mango', 'Apple', 'Orange', 'Banana' ]

16. sort

sort() method is used to sort the elements of the array. The sort order can be alphabetical or numerical, and in ascending or descending order.

// sortfunction: 可选。规定排序顺序。必须是函数。
array.sort(sortfunction)

let fruits = ["Banana", "Orange", "Apple", "Mango"]
let ages = [9, 3, 4, 5, 7, 10]
// 升序
let agesFunAsc = function (ag1,ag2) {
  return ag1 - ag2
}
// 降序
let agesFunDes= function (ag1,ag2) {
  return -(ag1 - ag2)
}
fruits.sort()
ages.sort(agesFunAsc)
console.log(fruits)
console.log(ages)
ages.sort(agesFunDes)
console.log(ages)
// [ 'Apple', 'Banana', 'Mango', 'Orange' ]
// [ 3, 4, 5, 7, 9, 10 ]
// [ 10, 9, 7, 5, 4, 3 ]

17. toString

toString() method is used to convert numbers to strings.

number.toString(radix)

let num = 15
let n = num.toString()
// 也可以使用不同的进制把一个数字转换为字符串
// 2进制
let b = num.toString(2);
// 8进制
let c = num.toString(8);
// 16进制
let d = num.toString(16);
console.log(n)
console.log(b)
console.log(c)
console.log(d)
// 15
// 1111
// 17
// f

18. at

at() method accepts an integer value and returns the value of the at index, both positive and negative integers are acceptable. A negative integer means counting down from the last item in the array.

array.at(index)

let str = 'helso word'
let item1 = str.at(2)
let item2 = str.at(-1)
console.log(item1)
console.log(item2)
// l
// d

19. find

find() method returns the value of the first element of the array that passes the test (judged within the function).

array.find(function(currentValue, index, arr),thisValue)

let ages = [3, 10, 18, 20];
function checkAdult(age) {
  return age >= 18;
}
let value = ages.find(checkAdult)
console.log(value)
// 18

20. some

some() method is used to detect whether the elements in the array meet the specified conditions (provided by the function).

array.some(function(currentValue,index,arr),thisValue)

rrree

The above is the detailed content of Summary of 20 common JavaScript array operations. For more information, please follow other related articles on the PHP Chinese website!