Summary of Common Methods of js Array and String

  • 2021-07-10 18:47:15
  • OfStack

Recently, I have been combing the basics of js, starting with arrays and strings.

Common methods of string:

1. The position truncated by substring (index of the beginning position of start, index of the end position of end) does not contain the character of the end position, and only writes 1 parameter to indicate that it is truncated from the beginning position to the end


   var str='abcdefg';  
   str.substring(1) // Get bcdefg  str.substring(1,3) // Get bc

When you enter a negative value, change the negative value to 0, which is the smaller as the starting position

str.substing(-1,1) = > str.substring(0,1) //a
str.substring(1,-2) = > str.substring(0,1) //a

2. slice (start start position index, end end position index) is basically similar to substring, except that the parameter is negative.


var str='abcdefg'; 
str.slice(1)  //bcdefg      str.substring(1,3) // bc

Add the value to the length of the string when you enter a negative value

str.slice(-1) = > str.slice(6) //g
str.slice(1,-2) = > str.slice(1,5) //bcde
str.slice(-2,-1)= > str.slice(5,6) //f

Value becomes 0 when its absolute value is greater than the length of the string

str.slice(-22) = > str.substring(0) //abcdefg

Returns ''when the absolute value of the second parameter is greater than the length of the string

3. substr (index of starting position of start, number of characters that end needs to return)


var str='abcdefg'; 
str.substr(1) //bcdefg      str.substr(1,1) //b

When a negative value is entered, the start parameter is added to the length of the string, and when end is negative, the parameter becomes 0


 str.substr(-1) =>str.substr(6)//g         
 str.substr(-2,-3) // ''

4. The charAt (index) method returns the character at the specified index position. If the index value exceeds the valid range (0 and string length minus 1), it returns an empty string.


 var str='abcdefg';
 str.charAt(2) // c

5. index (string) returns the first occurrence of a substring within an String object. If no substring is found,-1 is returned.

 var str='abcdefga'  str.indexOf('a')  // 0   str.indexOf('h') //-1

6. lastIndexOf (string) flashback lookup

Returns the first occurrence of a substring within an String object. If no substring is found,-1 is returned.

var str='abcdefga'     str.lastIndexOf('a') // 7

7. split (str) Splitting strings into arrays with parameters

var str='abcadeafg'     str.split('a') //["", "bc", "de", "fg"]

8. The toLowerCase method returns a string in which the letters are converted to lowercase.

9. The toUpperCase method returns a string in which all letters are converted to uppercase.

10. The match () method retrieves a specified value within a string or finds a match for one or more regular expressions

11. The search method returns the position of the first string that matches the regular expression lookup.

12. replace is used to find a string that matches 1 regular expression, and then replaces the match with a new string

http://www.cnblogs.com/bijiapo/p/5451924.html

Common methods of arrays

1. push is added to return the added array at the end

2. unshift added to the front returns the added array

3. shift Delete (from the front) returns the processed array

4. pop Delete the last entry and return the processed array

5. reverse array flipping returns the processed array

6. join Array Converted to String


   var arr=[1,2,3,4,5], str=arr.join('--'); 
    console.log(str); // 1--2--3--4--5  With join Cut the array with parameters in the 
    console.log(arr); // [1,2,3,4,5]   The original array remains unchanged 

7. slice (start, end) truncates an array from start (beginning) to end (end not included)

Returns a new array, leaving the original array unchanged


    var arr=[1,2,3,4,5],new=arr.slice(2,4);
    console.log(new);  // [3,4]
    console.log(arr);  // [1,2,3,4,5]     

8. concat combinations and

9. splice (start subscript, number, ele1, ele2...) splice array

(1). 1 parameter is truncated from the parameter position and filled in negative numbers similar to the above str slice returns the truncated array change of the original array


     var arr=[1,2,3,4,5];
     console.log(arr.splice(1));  // [2,3,4,5]
     console.log(arr);       // [1]
     console.lgo(arr.splice(-1))  // [5]    

(2). 2 Parameter truncation (starting position, number) returns the truncated array change of the original array


     var arr=[1,2,3,4,5];
     console.log(arr.splice(1,3)); // [2,3,4]
     console.log(arr)       // [1,5]
     arr.splice(0,1) =>arr.shift()
     arr.splcie(arr.length-1,1) =>arr.pop()

(3). Add the original array to add


     var arr=[1,2,3,4,5];
     console.log(arr.splice(1,0,13)); // []
     console.log(arr);        // [1,13,2,3,4,5]

(4). Replacement


var str='abcdefg'; 
str.slice(1)  //bcdefg      str.substring(1,3) // bc
0

10. arr. forEach (item, index, array) {} traverses, loops each similar to jquery

Where the item parameter is the contents of the array, index is its index, and array is the array itself


var str='abcdefg'; 
str.slice(1)  //bcdefg      str.substring(1,3) // bc
1

There is a problem in nested jump-out loop, which has not been solved for the time being;

11. map method mapping usage is similar to forEach


var str='abcdefg'; 
str.slice(1)  //bcdefg      str.substring(1,3) // bc
2

12. arr. sort Sequencing


  var arr=[1,2,22,11,33,3,5,4];
    console.log(arr.sort()) // [1,11,2,22,3,33,4,5] 

By default, the sort method is sorted by ascii alphabetical order, not by number size as we think

arr.sort(function(a,b){ return a-b})

a-b from small to large b-a from large to small

13. By the way, write about the sorting methods I know

(1) Bubble sorting compares two adjacent numbers every time. If the last one is smaller than the previous one, change the position


var str='abcdefg'; 
str.slice(1)  //bcdefg      str.substring(1,3) // bc
4

(2) Quick sort 2 points method, find the middle number, take out (new array), the original array does not, every time compared with this number, small to the left, big to the right


var str='abcdefg'; 
str.slice(1)  //bcdefg      str.substring(1,3) // bc
5

14. Write down the de-duplication of the array

(1) The double-layer cycle is not very good


var str='abcdefg'; 
str.slice(1)  //bcdefg      str.substring(1,3) // bc
6

(2) No duplication of key using json


var str='abcdefg'; 
str.slice(1)  //bcdefg      str.substring(1,3) // bc
7

(3) Sort by sort method, and remove the same items next to it


   var arr=[2,3,2,4,4,4,5],
      arr2=[];
        arr.sort();
        for(var i=0;i<arr.length;i++){
          if(arr[i]==arr[i+1]){
            arr.splice(i--,1);
          }
        }

1 Some common mathematical methods


var str='abcdefg'; 
str.slice(1)  //bcdefg      str.substring(1,3) // bc
9

Some Comprehensive Applications of Array and String

1. Intercept suffix names

(1) var str='1.xxx.avi';

str=str.substring(str.lastIndexOf('.')+1);

(2) var str='1.xxx.avi';


        var arr=str.split('.');
        console.log(arr[arr.length-1]);

2. The letters are flipped and the first letter is capitalized


     var str='wo shi yi ge demo',
        arr=str.split(' ');
        for(var i=0;i<arr.length;i++){
          console.log()
         arr[i]=arr[i].charAt(0).toUpperCase()+arr[i].substring(1);
        }
        arr.reverse();
        str=arr.join(' ');

3. Statistics of Character Occurrence in str


     var str='aaaandkdffsfsdfsfssq12345',
        json={},
        n= 0,
        sName;
        for(var i= 0,len=str.length;i<len;i++){
          var Letter=str.charAt(i);
          // Statistical times 
          if(json[Letter]){
            json[Letter]++;
          }else{
            json[Letter]=1;
          }
        }
        // Find the biggest 
        for(var name in json){
          if(json[name]>n){
            n=json[name];
            sName=name;
          }
        }
        console.log(' The letters that appear the most '+sName+' The number of times is '+n);

4. Simple parsing of url parameters


var str='abcdefg'; 
str.substr(1) //bcdefg      str.substr(1,1) //b
3

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