当前位置:网站首页>JS string - string string object method
JS string - string string object method
2020-11-06 22:11:37 【The front end of the attack】
Ⅰ- one -String String type
One String How to create
- How to create literal quantity , In stack
- Instantiation creation method ,(new) In stack
- How to create constructors , Will create a character object , In the pile
- A string of length Gets the length of the string . It's just readable Do not modify Can only get
- str.charAt(1) Equate to str[1]
// How to create literal quantity
var str="abc",str1='abd',str2=`abc`;
// Instantiation creation method
var str4=String('abc');// In stack
// How to create constructors
var str5=new String('abc');// Character objects , In the pile
console.log(str4===str5);//false
console.log(str4==str5);//true
Two Basic packaging type
To facilitate the operation of basic data types , JavaScript Three special reference types are also provided : String、Number and Boolean.
The basic wrapper type is to wrap a simple data type into a complex data type , So the basic data type has properties and methods .
- Objects have properties and methods Complex data types have properties and methods
- Why simple data types have lenght Attribute? ?
- Basic packaging type : It's wrapping simple data types into complex data types
// Basic packaging type
varstr='andy';
console. log(str .length);
// Objects have properties and methods Complex data types have properties and methods
// Why simple data types have lenght Attribute? ?
// Basic packaging type : It's wrapping simple data types into complex data types
// (1) Wrapping simple data types into complex data types
var temp=new String('andy' );
// (2) Give the value of the temporary variable to str
str = temp;
// (3) Destroy this temporary variable
temp=nul1:
3、 ... and String The immutability of string
It means that the values in it are immutable , Although it seems that the content can be changed , But the address has changed , A new memory space has been opened up in memory .
- When you give str When you assign , Constant ’abc’ Will not be modified , Still in memory
- Reassign string , Will re open up space in memory , This feature is the immutability of strings
- Because of the immutability of string , There are efficiency problems when splicing a large number of strings ;
var str = 'abc' ;
str = 'hello';
// When you give str When you assign , Constant 'abc' Will not be modified , Still in memory
// Reassign string , Will re open up space in memory , This feature is the immutability of strings
// Because of the immutability of string , There are efficiency problems when splicing a large number of strings ;
var str= ‘’;
for(vari=0;i<100000;i++){
str += i;
}
console.log(str); // This result takes a lot of time to show , Because we need to constantly open up new space
Ⅱ - Ii. -String String object method
length Gets the length of the string
let myString = "hello kitty";
myString.length; // Output 11
One Return position according to character
String all methods , Will not modify the string itself ( Strings are immutable ) , The operation will return a new string .
Method name | explain |
---|---|
indexOf( Characters to find , Starting position ) | Returns the location of the specified content in the meta string , If you can't find it, go back -1, The starting position is index Reference no. |
lastindexOf() | Look backwards , Just find the first match |
1 indexOf
effect : Through the characters , Find the corresponding index and return
grammar :
character string .indexOf( The character you are looking for )
character string .indexOf( The character you are looking for , Which index to start with )
Return value : A number
If there is this character , Then it returns the index of the position of the first character found
If there is no such character , So return -1
let myString = "hello kitty";
myString.indexOf('kitty'); // 6
myString.indexOf('Hello'); //-1
myString.indexOf('hello'); //0
myString.indexOf('hello',3); //-1
//
var str = 'hello world';
// When you look for a character with more than one letter , It will find the position of the first letter that matches and returns
var res = str.indexOf('world');
console.log(res);// The result is 6
2 lastIndexOf()
effect : Through the characters , Find the corresponding index and return , Search back and forth
grammar :
character string .lastIndexOf( The character you are looking for )
character string .lastIndexOf( The character you are looking for , Which index to start with )
Return value : A number
If there is this character , Then it returns the index of the position of the first character found
If there is no such character , So return -1
let myString = "hello kitty";\
myString.lastIndexOf('hello') // 0
myString.lastIndexOf('world') // -1
myString.lastIndexOf('kitty') // 6
myString.lastIndexOf('kitty',3) // -1
//
var str = 'hello world';
// Look from right to left
var res = str.lastIndexOf('l');
console.log(res);// The result is 9
Two Returns the character according to the position
Method name | explain | Use |
---|---|---|
charAt(index) | Returns the character in the specified position (index The index number of the string ) | str.charAt(0) |
charCodeAt(index) | Gets the... Of the character at the specified location ASCII code (index Reference no. ) | str.charCodeAt(0) |
str[index] | Gets the character at the specified location | HTML5.IE8. and charAt() equivalent |
1 charAt()
char: character , Represents a character
at: Where is the
effect : Find the corresponding character according to the index and return
grammar : character string .charAt( Indexes )
Return value : The character corresponding to the index position
If there is a corresponding index , So what you get is the character corresponding to the index position
If there is no corresponding index , So what you get is An empty string
var str = 'hello world';
var res = str.charAt(8);
console.log(res);// The result is r , Spaces also occupy the index position
2 charCodeAt() and String.fromCharCode()
charCodeAt()
effect : Find the corresponding character according to the index , Returns the encoding of a character
grammar : character string .charCodeAt( Indexes )
Return value : The character code corresponding to the index position UTF-8 code
String.fromCharCode()
effect : According to the corresponding character , return Unicode Code the corresponding value
grammar :String.fromCharCode( The conversion Unicode code )
Return value : The character code corresponding to the index position UTF-8 code
var str = ' Hello The world ';
// res What you get is you The code of this Chinese character
var res = str.charCodeAt(1);
console.log(res);// The result is 22909 It's the code of this Chinese character
var rek = String.fromCharCode(res); // The encoding is converted to a string
console.log(rek)// The result is good
3、 ... and String operation method ( a key )
Method name | explain |
---|---|
concat(str1,str2,str3…) | concat() Method to connect two or more strings . String concatenation , Equivalent to +, + More commonly used |
substr(start,length) | from start Position start ( Reference no. ),length Take the number and remember this |
substring(start, end) | from start Position start , Intercept to end Location ,end There is no basic and slice Same but not negative |
replace() | Method is used to replace some characters with others in a string , Or replace a substring that matches a regular expression . |
match() | Method to retrieve the specified value in a string , Or find a match for one or more regular expressions . In an array |
search() | Used to retrieve the position of a specified substring in a string |
toUpperCase() | Method to convert a string to uppercase . |
toLowerCase() | Method to convert a string to lowercase . |
slice(start, end) | from start Position start , Intercept to end Location , end Can't get ( They're both index numbers ) |
split() | Cut string Returns an array after cutting Used in object Method join() Array to character contrary |
1 concat()
effect : String concatenation
grammar : character string .concat( The string to be spliced 1, The string to be spliced 2, …)
Return value : A concatenated string
Function and plus (+) It's exactly the same
let myString = "Hello kitty";
//concat()
let str = "aabbcc"
let str2 = " ccddeeff"
myString.concat(str) // "Hello kittyaabbcc"
myString.concat(str,str2) // "Hello kittyaabbcc ccddeeff"
//
var str = 'hello world';
var res = str.concat(' Hello The world ');
console.log(res);// The result is hello world Hello The world
2 substring() and substr()
Parameters do not support negative numbers
subbstring()
effect : Extract some content from the string
grammar : character string .substring( Start index , End index ) - The head is not the tail The second parameter does not write , Default to end
Return value : A new string , The content extracted from the original string
var str2 = 'hello world';
// From the index 1 Start , To the index 7, Index not included 7
var res2 = str2.substring(1, 7);
console.log(res2);// The result is ello w
substr()
effect : Extract some content from the string
grammar : character string .substr( Index started , How many? )
The second parameter does not write , By default, it is calculated according to the end of the string
Return value : A new string , The content extracted from the original string
var str = 'hello world';
// From the index 1 Start , Count back 7 individual , extracted
var res = str.substr(1, 7);
console.log(res);// The result is ello wo
3 split()
effect : According to your needs , Cut string
grammar : character string .split(‘ The characters you want to cut ’)
Parameters cut you according to what you write
If you write a character that is not in the string , So I'll cut you a whole string
If the parameter is not written , It's also about cutting a whole string
If you write a parameter An empty string (""), Will cut you one by one
You can only choose from the back to the front
Return value : It's a Array
Cut each part according to your rules , Put them in the array
let myString = "Hello kitty";
myString.split(""); // ["H", "e", "l", "l", "o", " ", "k", "i", "t", "t", "y"]
myString.split(" "); // ["Hello", "kitty"]
myString.split(" ")[0];//Hello character string Get data with zero subscript
let str2 = "23:34:56:78";
str2.split(":",3) // ["23", "34", "56"]
let str3 = "How,are,you,doing,today?"
str3.split(",") // ["How", "are", "you", "doing", "today?"]
var str = '2020-05-20';
// use - Separate strings , Each segment is placed in the array as a piece of data
var res = str.split('-');
console.log(res);// The result is ["2020", "05", "20"]
4 replace() Method is used to replace some characters with others in a string , Or replace a substring that matches a regular expression .
let myString = "Hello kitty";
myString.replace(/kitty/,"world") // "Hello world"
let name = "Doe, John";
name.replace(/(\w+)\s*, \s*(\w+)/, "$2 $1"); // "John Doe"
5 match() Method to retrieve the specified value in a string , Or find a match for one or more regular expressions .
let myString = "hello kitty";
myString.match("hello"); //hello
myString.match("Hello"); //null
let str = "2 plus 3 equal 5"
str.match(/\d+/g) //["2", "3", "5"]
6 slice()
slice And an array of slice equivalent
effect : Extract part of the data from a string
grammar :
character string .slice( Start index , End index ) - Not before, not after
character string .slice( Start index , Negtive integer )
When you write negative integers , Express character string .length + Negtive integer
Return value : A string , A part of a string that is extracted from the original string
var str = 'abcdefghijklmn';
// extract str Index in string 1 To the index 10 The characters of , Index not included 10
var res1 = str.slice(1, 10);
// You write -3 Equivalent to str.length + -3 === 11
var res2 = str.slice(1, -3);
var res3 = str.slice(1, 11);
console.log(res1);// The result is bcdefghij
console.log(res2);// The result is bcdefghijk
console.log(res3);// The result is bcdefghijk
7 toUpperCase() 、toLowerCase()
toUpperCase() Method to convert a string to uppercase .
effect : Convert all lowercase letters in a string to uppercase letters
grammar : character string .toUpperCase()
Return value : It's a converted String
var str2 = 'abcdefg';
var res2 = str2.toUpperCase();
console.log(res2);// The result is ABCDEFG
toLowerCase() Method to convert a string to lowercase .
effect : Convert all uppercase letters in a string to lowercase letters
grammar : character string .toLowerCase()
Return value : It's a converted String
var str = 'ABCDEFG';
var res = str.toLowerCase();
console.log(res);// The result is abcdefg
Four Case study
-
split Method can convert a string to an array , You can use the array method
-
conversely join It can also be converted to a string and can be used String method
1 url Intercept
1
function getURLPram(url){
url=url.split("?")[1];
var obj={
};
var arr=url.split("&");
for(var i=0;i<arr.length;i++){
var str=arr[i];
var arr1=str.split("=");
obj[arr1[0]]=arr1[1];
}
return obj;
}
2
function getURLPram(url){
return url.split("?")[1].split("&").reduce(function(value,item){
var arr=item.split("=");
value[arr[0]]=arr[1];
return value;
},{
})
}
var url="https://detail.tmall.com/item.htm?id=570063940353&ali_refid=a3_430406_1007:116401153:J:157145175_0_1069023083
var obj= getURLPram(url);
console.log(obj);
2 String flip
var str="abcdef";
// Convert to array , And then reverse , And then use "" Connect
str=str.split("").reverse().join("");
console.log(str);
版权声明
本文为[The front end of the attack]所创,转载请带上原文链接,感谢
边栏推荐
- C++ 数字、string和char*的转换
- C++学习——centos7上部署C++开发环境
- C++学习——一步步学会写Makefile
- C++学习——临时对象的产生与优化
- C++学习——对象的引用的用法
- C++编程经验(6):使用C++风格的类型转换
- Won the CKA + CKS certificate with the highest gold content in kubernetes in 31 days!
- C + + number, string and char * conversion
- C + + Learning -- capacity() and resize() in C + +
- C + + Learning -- about code performance optimization
猜你喜欢
-
C + + programming experience (6): using C + + style type conversion
-
Latest party and government work report ppt - Park ppt
-
在线身份证号码提取生日工具
-
Online ID number extraction birthday tool
-
️野指针?悬空指针?️ 一文带你搞懂!
-
Field pointer? Dangling pointer? This article will help you understand!
-
HCNA Routing&Switching之GVRP
-
GVRP of hcna Routing & Switching
-
Seq2Seq实现闲聊机器人
-
【闲聊机器人】seq2seq模型的原理
随机推荐
- LeetCode 91. 解码方法
- Seq2seq implements chat robot
- [chat robot] principle of seq2seq model
- Leetcode 91. Decoding method
- HCNA Routing&Switching之GVRP
- GVRP of hcna Routing & Switching
- HDU7016 Random Walk 2
- [Code+#1]Yazid 的新生舞会
- CF1548C The Three Little Pigs
- HDU7033 Typing Contest
- HDU7016 Random Walk 2
- [code + 1] Yazid's freshman ball
- CF1548C The Three Little Pigs
- HDU7033 Typing Contest
- Qt Creator 自动补齐变慢的解决
- HALCON 20.11:如何处理标定助手品质问题
- HALCON 20.11:标定助手使用注意事项
- Solution of QT creator's automatic replenishment slowing down
- Halcon 20.11: how to deal with the quality problem of calibration assistant
- Halcon 20.11: precautions for use of calibration assistant
- “十大科学技术问题”揭晓!|青年科学家50²论坛
- "Top ten scientific and technological issues" announced| Young scientists 50 ² forum
- 求反转链表
- Reverse linked list
- js的数据类型
- JS data type
- 记一次文件读写遇到的bug
- Remember the bug encountered in reading and writing a file
- 单例模式
- Singleton mode
- 在这个 N 多编程语言争霸的世界,C++ 究竟还有没有未来?
- In this world of N programming languages, is there a future for C + +?
- es6模板字符
- js Promise
- js 数组方法 回顾
- ES6 template characters
- js Promise
- JS array method review
- 【Golang】️走进 Go 语言️ 第一课 Hello World
- [golang] go into go language lesson 1 Hello World