Learn the basics of JavaScript string objects in one article

Basic concepts

Basic packaging types: wrap simple data types into complex data types. (Basic data types have properties and methods)

var str='andy';
console.log(str.length);

• wrap simple data types into complex data types

var temp=new String('andy');

• give the value of the temporary variable to str

str=temp;

• destroy the temporary variable

temp=null;

JavaScript provides Three special reference types: string, number, boolean.

• Strings are immutable.

Do not splice a large number of strings, because the original strings are also in memory. The value inside does not change. Although it seems that the content can be changed, in fact, the address has changed and a new memory space has been opened in the memory.

that return a string based on character position

will not modify the string itself (strings are immutable), and a new string will be returned when the operation is completed.

1. indexOf('character to be found', [starting position])

searches from front to back

var str="You are my God";
console.log(str.indexOf('I');//2
console.log(str.indexOf('I',1);

2. lastIndexOf('Character to be found', [starting position])

Search from back to front

var str="You are my God";
console.log(str.lastIndexOf('I');

returns character

1 according to the position, charAt (index number)

returns the character at the specified position

var str="andy";
console.log(str.charAt(3));

2. Traverse all characters

for(var i=0;i<str.length;i++){
 console.log(str.charAt(i));
}

3. charCodeAt (index number)

returns the ASCII code, which can be used to determine which key the user pressed.

console.log(charCodeAt(o));

4. str[index]

is new in H5 and has compatibility issues.

String operation method

1. concat('String 1', 'String 2',...)

var str=' cindy';
console.log(str.concat('red');

2. substr(start,length)

takes the length of characters starting from start

var str='You are my God';
console.log(str.substr(2,2));

3. Replace character replace('replaced character','replaced character')

only replaces the first character

var str='andandand';
console.log(str.replace('a','b');//bndandand

4. Convert characters to array split('separator')

var str='red,pink,blue';

console.log(str.split('&'));

5. toUpperCase() is converted to uppercase

6. toLowerCase() is converted to lowercase

A simple case

• to find the position and number of occurrences of all g in 'abcdefgabcdefg'

var str='abcdefgabcdefg';
        var index=str.indexOf('g');
        varnum=0;
        while(index!==-1){
            console.log(index);
            num++;
            index=str.indexOf('g',index+1);
        }
        console.log('The number of occurrences of g is:'+num);

• Determine the character that appears the most in a string 'abcdefgabcdefg', and count the number of times

var str='abcdefgabcdefg';
       var obj={};
       for(var i=0;i<str.length;i++){
           var chars=str.charAt(i);
           if(obj[chars]){

            obj[chars]++;
           }else{
               obj[chars]=1;
           }
       }
       console.log(obj);
       var max=0;
       var ch='';
       for(var k in obj){
           if(obj[k]>max){
               max=obj[k];
               ch=k;
           }
       }
       console.log(max);
       console.log('The most characters are '+ch);

• 'abcoefoxyozzoopp' replace o with *

var str='abcoefoxyozzoopp';
        while(str.indexOf('o')!==-1){
            str=str.replace('o','*');
        }
        console.log(str);