Summary of common methods and attributes of arrays and strings in JS

String Object properties

attribute	describe
length	Length of string
prototype	Allows you to add properties and methods to an object

length

length： Length of character creation

<script>
var str = "Hello World!";
document.write(txt.length);
</script>

result ：12

String Object methods

attribute	describe
charAt()	Returns the character in the specified position .
charCodeAt()	Returns the... Of a character in a specified position Unicode code .
concat()	Connect two or more strings , And return the new string .
endsWith()	Determines whether the current string ends with the specified substring （ Case sensitive ）.
fromCharCode()	take Unicode Code to character .
indexOf()	Returns the first occurrence of a specified string value in a string .
includes()	Find if the string contains the specified substring .
lastIndexOf()	Search string from back to front , And from the beginning （0） Start calculating the last occurrence of the return string .
match()	Find a match for one or more regular expressions .
repeat()	Copy string specified number of times , And connect them back together .
replace()	Find the matching substring in the string , And replace the substring that matches the regular expression .
replaceAll()	Find the matching substring in the string , And replace all substrings that match the regular expression .
search()	Find the value that matches the regular expression .
slice()	Extract a fragment of a string , And return the extracted part in the new string .
split()	Split a string into an array of strings .
startsWith()	See if the string starts with the specified substring .
substr()	Extract the specified number of characters in the string from the starting index number .
substring()	Extract the character between two specified index marks in the string .
toLowerCase()	Convert string to lowercase .
toUpperCase()	Convert strings to uppercase .
trim()	Remove the white space on both sides of the string .
toLocaleLowerCase()	Convert strings to lowercase according to the locale of the local host .
toLocaleUpperCase()	Convert strings to uppercase based on the locale of the local host .
valueOf()	Returns the original value of a string object .
toString()	Returns a string .

chartAt（）

chartAt（） Returns the character in the specified position

var str = "HELLO WORLD";
var n = str.charAt(2);
console.log(n)

result ：L

concat()

concat() Connect two or more strings

function myFunction(){
    
	var txt1 = "Hello ";
	var txt2 = "world!";
	var txt3="NI HAO";
	var n=txt1.concat(txt2,txt3);
	document.getElementById("demo").innerHTML=n;
}
</script>

result ：Hello world!NI HAO

endsWith（）

endsWith（） Judge whether the current string ends with the specified string

let str = "Hello world";
str.endsWith("world")   //  return  true
str.endsWith("World")   //  return  false

startsWith（）

startsWith（） Judge whether the current string starts with the specified string

var str = "Hello world, welcome to the Runoob.";
var n = str.startsWith("Hello");

result ：true

indexOf（）

indexOf（） Returns the first occurrence of a string in this string , If not found, put it back false

var str="Hello world";
var n=str.indexOf("world");

result ：6

repeat（）

repeat（） Copy string specified number of times , And connect them back together

var str = "Runoob";
str.repeat(2);

result ：RunoobRunoob

replace（）

replace（） Find the matching substring in the string , And replace the matching substring . In this case , We will perform a replacement , When the first one “Microsoft” Found , It is replaced by “Runoob”：

var str="Visit Microsoft! Visit Microsoft!";
var n=str.replace("Microsoft","Runoob");

result ：Visit Runoob!Visit Microsoft!

replaceAll（）

replaceAll（） Find the matching substring in the string , And replace all matching substrings .. In this case , We will perform a replacement , Find all “Microsoft” , Replace with “Runoob”：

var str="Visit Microsoft! Visit Microsoft!";
var n=str.replaceAll("Microsoft","Runoob");

result ：Visit Runoob!Visit Runoob!

serach（）

serach（） Find the value that matches the regular expression .

var str="Visit Runoob!"; 
var n=str.search("Runoob");

 result ：6
// Perform a case sensitive lookup :
var str="Mr. Blue has a blue house";
document.write(str.search("blue"));
// result ：15

// Perform a case insensitive Retrieval :
var str="Mr. Blue has a blue house";
document.write(str.search(/blue/i));
// result ：4

slice（）

slice（start,end） Intercepting string Return the extracted part in the new string
start: Start with the number of bits in the string
end: To the end of the string （ barring end）

var str="Hello world!";
var n=str.slice(1,5);
// result ：ello

// Extract all strings :
var str="Hello world!";
var n=str.slice(0);
// result ：Hello world!

// From the first... Of the string 3 Extract the string fragment at three positions :
var str="Hello world!";
var n=str.slice(3);
//lo world!

// From the first... Of the string 3 Position to 8 A direct string fragment :
var str="Hello world!";
var n=str.slice(3,8);
 result ：lo wo（ Note that the last one is not included ）


// Extract the last character and the last two characters 
var str="Hello world!";
var n=str.slice(-1);
var n2=str.slice(-2);
// result  !
// result  d!

split()

split（） Split a string into an array of strings .

 Divide a string into an array of strings : Note that the middle is separated by a space 
var str="How are you doing today?";
var n=str.split(" ");
// result ：How,are,you,doing,today?

// Split each character , Including Spaces :
var str="How are you doing today?";
var n=str.split("");
// result ：H,o,w, ,a,r,e, ,y,o,u, ,d,o,i,n,g, ,t,o,d,a,y,?

// Use  limit  Parameters :
var str="How are you doing today?";
var n=str.split(" ",3);
// result ：How,are,you

// Use a character as a separator :
var str="How are you doing today?";
var n=str.split("o");
// result ：H,w are y,u d,ing t,day?

substr（）

substr（1,2） Intercepts a specified number of characters , The first parameter is the number of characters , The second parameter is to intercept several characters

// Extract a specified number of characters ：
var str="Hello world!";
var n=str.substr(2,3)
// result ：llo

// In this case , We will use  substr()  Extract some characters from the second position of the string ：
var str="Hello world!";
var n=str.substr(2)
// result ：llo world!

substring()

substring（1,2） Intercepts a specified number of characters , The first parameter is the number of characters , The second parameter is the cut-off, and the number of parameters ends , Note that the last one is not included

// Extract a specified number of characters ：
var str="Hello world!";
var n=str.substr(2,3)
// result ：l

toLowerCase()

toLowerCase（） ： String to lowercase

toUpperCase()

toUpperCase（）： String to uppercase .

trim ()

trim （） ： Except for the blank space on both sides of the string .

toString ()

toString （） ： Returns a string .

Aarry

attribute	describe
length	Sets or returns the number of array elements .

Aarry.length

length

var fruits = ["1", "d", "f", "h"];
console.log(fruits.length);

result ：4

Array Object methods

attribute	describe
concat()	Two or more arrays , And return the result .
copyWithin()	Copy elements from the specified location of the array to another specified location of the array .
entries()	Returns the iteratable object of the array .
every()	Checks whether each element of a numeric element is eligible .
fill()	Fill the array with a fixed value .
filter()	Detect value elements , And returns an array of all elements that meet the criteria .
find()	Return compliance with incoming test （ function ） Conditional array elements .
findIndex()	Return compliance with incoming test （ function ） Conditional array element index .
forEach()	Each element of the array performs a callback function .
from()	Create an array from the given object .
includes()	Determine whether an array contains a specified value .
indexOf()	Search for elements in the array , And return to where it is .
isArray()	Determine whether the object is an array .
join()	Put all the elements of the array into a string .
keys()	Returns the iteratable object of the array , Contains the key of the original array (key).
lastIndexOf()	Search for elements in the array , And return to where it last appeared .
map()	Handle each element of the array by specifying a function , And return the processed array .
pop()	Delete the last element of the array and return the deleted element .
push()	Add one or more elements... To the end of the array , And returns the new length .
reduce()	Evaluate an array element to a value （ From left to right ）.
reduceRight()	Evaluate an array element to a value （ From right to left ）.
reverse()	Reverse the order of elements in an array .
shift()	Delete and return the first element of the array .
slice()	Pick a part of the array , And return a new array .
some()	Check whether any element in the array element meets the specified conditions .
sort()	Sort elements of an array .
splice()	Add or remove elements from an array .
toString()	Convert an array to a string , And return the result .
unshift()	Add one or more elements to the beginning of an array , And returns the new length .
valueOf()	Returns the original value of the array object .

concat（）

concat(arry): Concatenate two arrays

function myFunction(){
    
	var arr1= [1,2,3,4]
	var arr2= ["a","b"];
	var arr3=[6,7];
arr1.concat(arr2,arr3)
}
</script>

result ：1,2,3,4,a,b,6,7

copyWithin（）

Copy elements from the specified location of the array to another specified location of the array
Parameters ---------------- describe
target-------------- It's necessary . Copy to the specified target index location .
start---------------- Optional . The starting point of element copying .
end------------------ Optional . Stop copying index location ( The default is array.length). If it's negative , Said the bottom .

var fruits = ["Banana", "Orange", "Apple", "Mango", "Kiwi", "Papaya"];
fruits.copyWithin(2, 0, 2);

j result ：Banana,Orange,Banana,Orange,Kiwi,Papaya

entries（）

entries() Method returns the iterated object of an array , This object contains the key value pairs of the array (key/value). Is to change the object you create into key And value In the form of

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.entries();

result ：
[0, “Banana”]
[1, “Orange”]
[2, “Apple”]
[3, “Mango”]

every（）

every(): Check whether all elements of the array meet the conditions

var ages = [32, 33, 16, 40];

function checkAdult(age) {
    
    return age >= 18;
}

function myFunction() {
    
    document.getElementById("demo").innerHTML = ages.every(checkAdult);
}

result ：false

fill()

fill(): Fill the array with a fixed value .

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.fill("Runoob");

result ：Runoob,Runoob,Runoob,Runoob

filter()

filter(): Detect value elements , And returns an array of all elements that meet the criteria .

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

result ：32,33,40

find()

find(): Return compliance with incoming test （ function ） Conditional array elements .

var ages = [3, 10, 18, 20];

function checkAdult(age) {
    
    return age >= 18;
}

console.log(ages.find(checkAdult))

result ：18

findIndex()

findIndex()： Get the index position of the first element in the array that meets the condition

var ages = [3, 10, 18, 20];
 
function checkAdult(age) {
    
    return age >= 18;
}
 
function myFunction() {
    
    document.getElementById("demo").innerHTML = ages.findIndex(checkAdult);
}

result ：2

forEach()

forEach(): Loop traversal

numbers.forEach(myFunction)

from（）

from(): Create an array from the given object

var arr = Array.from([1, 2, 3], x => x * 10);
// arr[0] == 10;
// arr[1] == 20;
// arr[2] == 30;

includes()

includes(): Determine whether an array contains a specified value .

let site = ['runoob', 'google', 'taobao'];
 
site.includes('runoob'); 
// true 
 
site.includes('baidu'); 
// false

indexOf()

indexOf() Search for elements in the array , And return to where it is .

var fruits = ["Banana", "Orange", "Apple", "Mango"];
var a = fruits.indexOf("Apple");``` ** result ：2** # isArray() >isArray(): Determine whether the object is an array  ```javascript
 var fruits = ["Banana", "Orange", "Apple", "Mango"];
 var  x = Array.isArray(fruits);

result ：true

join()

join(): Put all the elements of the array into a string .

var fruits = ["Banana", "Orange", "Apple", "Mango"];
var energy = fruits.join();

result ：Banana,Orange,Apple,Mango

lastIndexOf（）

lastIndexOf(): Find the position of an element in the array element

var fruits=[" Banana "," The oranges "," Apple "," melon "];
var a=fruits.lastIndexOf(" Apple ")
console.log(a)

result ：true

map()

map(): Handle each element of the array by specifying a function , And return the processed array .

// Returns an array , The elements in the array are the square root of the original array :
var numbers = [4, 9, 16, 25];
var a=numbers.map(Math.sqrt);
console.log(a)

result ：2,3,4,5

pop()

pop(): Delete the last element of the array and return the deleted element

push()

push(): Add one or more elements... To the end of the array , And returns the new length .

reduce()

reduce(): Evaluate an array element to a value （ From left to right ）.

reduceRight()

reduceRight(): Evaluate an array element to a value （ From right to left ）.

shift()

shift() : Delete and return the first element of the array .

slice()

slice(): Pick a part of the array , And return a new array .

var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var myBest = fruits.slice(-3,-1); //  Intercept the penultimate （ contain ） To the last one （ It doesn't contain ） Two elements of 
var myBest = fruits.slice(-3);  //  Intercept the last three elements 

result ：Lemon,Apple

some()

some(): Check whether any element in the array element meets the specified conditions .

var ages = [3, 10, 18, 20];

function checkAdult(age) {
    
    return age >= 18;
}
console.log(ages.some(checkAdult));

sort()

sort()L: Sort elements of an array

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.sort();

splice()

splice(): Add or remove elements from an array .

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2,0,"Lemon","Kiwi");
//Banana,Orange,Lemon,Kiwi,Apple,Mango

// Remove the third element of the array , And add a new element in the third position of the array :
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2,1,"Lemon","Kiwi");
//Banana,Orange,Lemon,Kiwi,Mango

// Starting from the third position, delete the two elements after the array ：
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2,2);
//Banana,Orange

toString()

toString(): Array to string ：

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.toString();

result ：Banana,Orange,Apple,Mango

unshift()

unshift(): Add one or more elements to the beginning of an array , And returns the new length .

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon","Pineapple");

result ：Lemon,Pineapple,Banana,Orange,Apple,Mango

valueOf()

valueOf(): Returns the original value of the array object