Catalog

String - JavaScript | MDN

One . Access string characters

Two . String traversal

1 -  Normal cycle

2 - for...of loop

3、 ... and .  Modify string

Four . toUpperCase : Make all characters uppercase

5、 ... and . toLowerCase : Change all characters to lowercase

6、 ... and . Find string

1 - indexOf ( searchString , fromIndex ) : lookup

2 - includes( searchString , position ) : lookup

3 - startsWith : With xxx start

4 - endsWith : With xxx ending

7、 ... and . replace : Replace string

8、 ... and . Get substring  

Nine . String concatenation

1 - + 

2 - concat

Ten . trim : Delete the first and last strings

11、 ... and . split( swparator,limit ) :  String segmentation  

String - JavaScript | MDN

One . Access string characters

const message = 'hello world'

console.log( message[1] ) // e
console.log( message.charAt(4) ) // o

Two . String traversal

1 -  Normal cycle

const message = 'hello world'

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

2 - for...of loop

// for..of The traversal  ->  iterator 
//  Currently iteratible objects :  character string / Array 
//  Object is not supported for..of
// String Inside the object is to turn the string into an iteratable object 

for (let char of message) {
  console.log(char)
}

3、 ... and .  Modify string

After the string definition is Cannot be modified Of , So when directly manipulating characters is invalid

let message = "Hello World"

message[2] = "A"
console.log(message) // Hello World.  It won't change 

Four . toUpperCase : Make all characters uppercase

const message = 'hello'

console.log(message.toUpperCase()) // HELLO , The original string has not changed , Instead, a new string is generated 

5、 ... and . toLowerCase : Change all characters to lowercase

const message = 'HeLLo'

console.log(message.toUpperCase()) // hello, The original string has not changed , Instead, a new string is generated 

6、 ... and . Find string

1 - indexOf ( searchString , fromIndex ) : lookup

• Situation 1 : Search for , The index position of the search string
• Situation two : No search for , return -1

const message = 'my name is coder'

let index = message.indexOf('name')
if(index !== -1){
    console.log(' eureka ')
}else{
    console.log(' Did not find ')
}

2 - includes( searchString , position ) : lookup

const message = 'my name is coder'

if(message.includes('name')){
    console.log(' eureka ')
}

3 - startsWith : With xxx start

const message = 'my name is coder'

if (message.startsWith("my")) {
   console.log("message With my start ")
}

4 - endsWith : With xxx ending

const message = 'my name is coder'

if (message.endsWith("coder")) {
   console.log("message With my ending ")
}

7、 ... and . replace : Replace string

• Find the corresponding string , And use the new string to replace
• You can also pass in a regular expression to find , You can also pass in a function to replace

//  Incoming string 
const message = 'my name is star'
let newMessage = message.replace("star", "kobe")
console.log(newMessage) // my name is kobe

//  Passing in functions 
const newName = "kobe"
let newMessage = message.replace("star", function() {
  return newName.toUpperCase()
})
console.log(newMessage) // my name is KOBE

8、 ... and . Get substring  

const message = "Hello World"

console.log(message.slice(3, 7)) // lo W
console.log(message.slice(3, -1)) // lo Worl
console.log(message.slice(3)) // lo World

console.log(message.substr(3, 7)) // lo Worl

Nine . String concatenation

1 - + 

const str1 = "Hello"
const str2 = "World"
const str3 = "kobe"

const newString = str1 + str2 + str3
console.log(newString)

2 - concat

const str1 = "Hello"
const str2 = "World"
const str3 = "kobe"

//  Chainable call 
const newString2 = str1.concat(str2).concat(str3)
//  Multiple values can be passed in at the same time 
const newString3 = str1.concat(str2, str3, "abc", "cba")

Ten . trim : Delete the first and last strings

console.log("    star      abc   ".trim()) // star      abc

11、 ... and . split( swparator,limit ) :  String segmentation  

• separator： What string to split , It can also be a regular expression ;
• limit： Limit the number of returned fragments ;

const message = "abc-cba-nba-mba"
//  The cutting character is  => -
const items = message.split("-")
console.log(items) // ['abc','cba','nba','mba']
//  By array join Method , Variable to string   The connecting character is  *
const newMessage = items.join("*")
console.log(newMessage) // abc*cba*nba*mba

//-----------------------------------------------

const message = 'abc-cba-nba-mba';
//  Return length is 2 Array of 
const items = message.split('-', 2);
console.log(items); // ['abc','cba']