String methods and instances

String method

  var str = "VFDrerDAVvszds" // Literal declaration string 
  // var str1=new String("sssssss") // Constructor mode declaration string 
  console.log(str.length); // length  Property returns the length of the string ：13

1. indexOf() Method returns the index of the first occurrence of the specified text in a string （ Location ）

console.log(str.indexOf("s")) //indexOf()  Method returns the index of the first occurrence of the specified text in a string （ Location ）10

2.lastIndexOf() Method returns the index of the last occurrence of the specified text in the string

console.log(str.lastIndexOf("s")); // lastIndexOf() Method returns the last occurrence of a specified string value 

If the element you are looking for is not found , indexOf() and lastIndexOf() All return to -1

3. search() Method to search for a string of specific values , And return to the matching position

 console.log(str.search("s")); // Search for a string of specific values , And return to the matching position 

4. slice(start,end) Extract a part of the string and return the extracted part in the new string

 console.log(str.slice(3, 5)); // Crop the position in the string  3 To the position  5  Fragments of  :re 

5. substring(start,end) Extract a part of the string and return the extracted part in the new string ( Cannot accept negative index )

console.log(str.substring(3,5));// Crop the position in the string  3 To the position  5  Fragments of  :re 

6. substr(start, length) from start The index begins to extract several strings of strings

console.log(str.substr(3,5));//rerDA

7. .replace() Method replaces the first matching value with another value , Does not change the string that calls it . It returns a new string

 console.log(str.replace("V", " you ")); // you FDrerDAVvszds

8. toUpperCase() Convert strings to uppercase

 console.log(str.toUpperCase());//VFDRERDAVVSZDS

9. adopt toLowerCase() Convert string to lowercase

 console.log(str.toLocaleLowerCase());//vfdrerdavvszds

10. concat() Concatenate two or more strings

    var str1 = "hello",str2 = "javaScript"
        var str3 = str1.concat(str2)
        console.log(str3);//hellojavaScript
        

11. trim() Method to delete the whitespace characters at both ends of a string

  var str=" swi "
        var str1=str.trim()
        console.log(str1);//swi

12.charAt() Method returns the specified subscript in the string （ Location ） String

var str = "HELLO JAVASCRIPT";
str.charAt(0);            //  return  H

13. Can pass split() Convert string to array

var txt = "a,b,c,d,e"; //  character string 
        console.log(txt.split(",")); // ["a", "b", "c", "d", "e"]  Separate with commas 

The following is an example of a string

The string method uses the middle four digits of the mobile phone number * Express

  <script>
        var str = '12133536409' 

        function mosaic(str, start, length) {
    
            let left = str.substring(0, start)
            // console.log(left); //121
            let middle = "*".repeat(length)
            // console.log(middle); //****
            let right = str.substring(start + length)
            // console.log(right);//6409
            return left + middle + right // Put the new number return come out 
        }
        console.log(mosaic(str, 3, 4)); //121****6409
    </script>

String length truncation

 function cut(str, length) {
    
            if (str.length < length) return str
            else
                return str.substr(0, length) + "..."
        }
        console.log(cut(" Hello , I'm the monkey king ", 5)); // Hello , I am a ...

Replace

let send = " Dear users [0] Hello! , Welcome to consult our products "
        let numlist = "13344445555,12233334444,16677778888"
        numlist.split(",").forEach(item => {
    
            console.log(send.replace("[0]", item));
        })

The input result is as follows