Related methods of strings in js

The underlying string is stored in the form of an array of characters

[“H” ”e” ”l” ”l” ”o”]

length attribute

• You can get the length of the string

//Create a string
var str = "Hello World"
console.log(str.length);
console.log(str[5]);

charAt( )

• Can return the character at the specified position in the string
• Get the specified character according to the index

//charAt() can return the character at the specified position in the string
var result = str.charAt(1);
console.log(result); Get the character with index 1

charCodeAt( )

• Can return the unicode encoding of the character at the specified position in the string

//charCodeAt() returns the unicode encoding of the character at the specified position in the string
var result2 = str.charCodeAt(0);
console.log(result2); returns the Unicode encoding of the character at index 0

String.formCharCode( )

• Characters can be obtained according to character encoding

// String.fromCharCode() can get the character according to the character code
var result3 = String.fromCharCode(72);
console.log(result3); returns the character with Unicode code 72

Concat（）

• You can concatenate two or more strings
• Same as +
• Will not affect the original string

//concat() can concatenate two or more strings
var str = "Hello World"
var result4 = str.concat("Hello, goodbye");
console.log(result4); concatenate two strings

indexOf( )

• This method can retrieve whether a string contains specified content
• If the string contains the content, the index of its first occurrence will be returned
• If the specified content is not found, it will return -1
• You can specify a second parameter to specify the location to start searching

//indexOf() can retrieve whether a string contains the specified content (from front to back)
var str = "Hello World"
var result5 = str.indexOf("e",1);
console.log(result5); from Find the character with e at the index of 1

lastIndexOf( )

• The usage of this method is the same as indexOf()
• The difference is that indexOf() is to find from front to back
  lastIndexOf() is to find from back to front
• You can also specify where to start the search

//lastIndexOf() can retrieve whether a string contains the specified content (search from back to front )
var str = "Hello World"
var result6 = str.lastIndexOf("l",5);
console.log(result6) from Start at index 5 to find the character that is l

Slice( )

• Can intercept the specified content from the string
• Does not affect the original string, but returns the intercepted content
• parameter
• Index of the first start position (including start position)
• The index of the second end position (not including the end position)
• If the second parameter is omitted, all the following will be intercepted
• You can also pass a negative number as a parameter, and the negative number will be calculated from the back

//slice() can intercept the specified content from the string
var str = "abcdefg";
var result = str.slice(0,3);
console.log(result); intercept the characters whose index is from 0 to 3

subString( )

It can also be used to intercept a string, similar to slice()

• parameter
• Index of the first start position (including start position)
• The index of the second end position (not including the end position)
• The difference is that this method does not accept negative value as a parameter
  , if a negative value is passed, the default 0
• And it also automatically adjusts the position of the parameter, if the second parameter is less than the first parameter, it will automatically exchange

subStr( )

• Used to intercept the string
• parameter
• Index of the first start position (including start position)
• The second intercepted quantity

//substr() intercepts the string, the second parameter indicates the number of interceptions
var str = "abcdefg";
var result = str.substr(3,2);
console.log(result); starting from the character whose index is 3 Intercept 3 characters

split( )

• You can split a string into an array
• parameter:
  • A string is required as a parameter, and the array will be split according to the string

//split() can split a string into an array
var str = "abc,def,ghi,jkl";
result = str.split(",");
console.log(typeof result);
console.log( result);
console.log(result.length);

toUpperCase( )

• Can convert the string to uppercase and return

//toUpperCase() can convert a string to uppercase
var str = "abcdefg";
result = str.toUpperCase();
console.log(result);

toLowerCase( )

• Can convert the string to lowercase and return

var str = “ABCDEFG”;
result = str.toLowerCase();
console.log(result);