String common methods

 

• String splicing ：

  • concat() ： String splicing

  let num = "1";
  let num1 = num.concat("2")
  console.log(num1) //"12"

• String delete ： Create a copy of the original string , Then delete the copy

  • slice(): Two parameters . The first is the starting position , The second is the end position

  • substr()： Two parameters . The first is the starting position , The second is the total number of elements

  • substring()： Two parameters . The first is the starting position , The second is the end position

  let stringValue = "hello world";
  console.log(stringValue.slice(3)); // "lo world"
  console.log(stringValue.substring(3)); // "lo world"
  console.log(stringValue.substr(3)); // "lo world"
  console.log(stringValue.slice(3, 7)); // "lo w"
  console.log(stringValue.substring(3,7)); // "lo w"
  console.log(stringValue.substr(3, 7)); // "lo worl"

• Modify string ： Create a copy of the original string , Then modify the copy

  • trim() : Remove all spaces before and after , And return the new string

  • trimLeft() : Delete all preceding spaces , And return the new string

  • trimRight() : Delete all the following spaces , And return the new string

  let str = " hello "
  let str1 = str.trim();
  console.log(str)  // " hello "
  console.log(str1) //"hello"

  • repeat(n) : Copy n Substring , Then all the results are spliced and returned

  let str = "name";
  let str1 = str.repeat(2) //name name

  • padStart(n): Copy string , If it is less than n, The character... Is added before the string

  let str = "name";
  let str1 = str.padStart(6, ".") // "..name"

  • padEnd(n): Copy string , If it is less than n, Then the character... Is added after the string

  let str = "name";
  let str1 = str.padStart(6, ".") // "name.."

  • toLowerCase() : Convert a string to lowercase

  let str = "ABC";
  let str1 = str.toLowerCase(); //"abc"

  • toUpperCase() : Convert a string to uppercase

  let str = "abc";
  let str1 = str.toLowerCase(); //"ABC" 

• To find the character

  • chatAt(n) : return n Characters in position

  let str = "abcde";
  let str1 = str.charAt(2); // "c"

  • indexOf() : Find the incoming string from the beginning , Return to the first Find the position of this string （ No return found -1）

  let str = "abcde";
  let str1 = str.charAt("b"); // 1

  • startWith() 、includes() : Find the incoming string from the string , If any, return true, Otherwise return to false

  let str = "abcdefg"
  let str1 = str.startWith("abcd") //true
  let str2 = str.includes("abcd") //true

• String to array ：split() : Split the string into an array according to the specified delimiter

let str = "abcd";
let str1 = str.split("") //[a, b, c, d]