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This is a supplement to the first two articles, with links attached.
Links with array contents: https://blog.csdn.net/m0_60263299/article/details/120789000?spm=1001.2014.3001.5501.
Links with object content: https://blog.csdn.net/m0_60263299/article/details/120901661?spm=1001.2014.3001.5501.

1, Array creation

How to create an array	Example content
Literal mode	var arr = [1,"test",true];
new Array()	var arr = new Array();

For specific cases, please click the link with array content below the expression package above.

be careful:

• In the above code, arr creates an empty Array. If you need to use the constructor Array to create a non empty Array, you can pass in parameters when creating the Array.

The parameter transfer rules are as follows:

• If only one parameter is passed in, the parameter specifies the length of the array.
• If more than one parameter is passed in, the parameter is called an element of the array.

2, Detect whether it is an array

2.1 instanceof operator

• instanceof can determine whether an object is an instance of a constructor.
• The code is as follows (example):

   var arr = [1, 23];
   var obj = {};
   console.log(arr instanceof Array); // true
   console.log(obj instanceof Array); // false

2.2 Array.isArray()

• Array.isArray() is used to determine whether an object is an Array.isArray() is a method provided in HTML5.
• The code is as follows (example):

   var arr = [1, 23];
   var obj = {};
   console.log(Array.isArray(arr));   // true
   console.log(Array.isArray(obj));   // false

3, Methods for adding and deleting array elements

3.1 method of adding array elements

• push() adds one or more array elements to the end of our array and returns the length of the new array.

• unshift() adds one or more array elements at the beginning of our array and returns the length of the new array.

3.2 method of deleting array elements

• pop() can delete the last element of the array and return the deleted element.

• shift() can delete the first element of the array and return the deleted element.

4, Array sorting

The code is as follows (example):

    //Array sorting
    //1. Flip array
    var arr = ['pink', 'red', 'blue'];
    arr.reverse();
    console.log(arr);

    //2. Array auction (bubble sort)
    var arr1 = [3, 11, 7, 1, 13, 77];
    arr1.sort(function(a, b) {
        return a - b; //In ascending order
        // return b - a; // In descending order
    });
    console.log(arr1);

5, Array index method

The code is as follows (example):

    var arr = ['red', 'green', 'blue', 'pink'];
    console.log(arr.indexOf('blue'));        // Return result 2
    console.log(arr.lastIndexOf('pink'));    // Return result 3

6, Convert array to string

method	content
toString()	Convert the array into a string, and separate each item with a comma; Returns a string
join()	Used to convert all elements in the array into a string; Returns a string
concat()	Connect two or more arrays without affecting other arrays; Returns a new array
slice()	Array interception slice (begin, end); Returns the intercepted new array
splice()	Delete the slice of the array (the number of deleted from the first few); Return the core array of deleted items, which will affect the original array

7, String object

7.1 string operation method

The code is as follows (example):

    //1.concat('string 1 ',' string 2 '...)
    var str = 'andy';
    console.log(str.concat('red'));
    //2.substr('intercept start position ',' intercept several characters'...)
    var str1 = 'The spring breeze of reform is blowing';
    console.log(str1.substr(2, 2)); //The first 2 is the 2 of the index number, starting from the first few; How many characters does the second 2 take

7.2 return position according to characters

The code is as follows (example):

    var str = 'The spring breeze of reform is blowing all over the ground, and spring is coming';
    console.log(str.indexOf('spring'));
    console.log(str.indexOf('spring', 3)); //Look up from where the index number is 3

7.3 return characters according to position

The code is as follows (example):

    //(1) charAt(index) 
    var str = 'andy';
    console.log(str.charAt(3));
    //Traverse all characters
    for (var i = 0; i < str.length; i++) {
        console.log(str.charAt(i));
    }
    
    //(2) charCodeAt(index) returns the character ASCII code of the corresponding index number
    //Objective: to determine which key the user pressed
    console.log(str.charCodeAt(0)); //97

    //(3) str[index] gets the character at the specified position
    console.log(str[0]); //a

7.4 replace() method

• The replace() method is used to replace some characters with others in a string.
• replace('replaced character ',' replaced character ');

7.5 split() method

• The split() method is used to split strings, which can be split into arrays. After segmentation, a new array is returned.
• String. split("split character");

summary

Learning diary is a good way to consolidate knowledge, but it's a bit of a waste of time. In the future, I hope to change from introducing basic knowledge to introducing problems encountered or solving problems, but the basic knowledge should be consolidated and rushed.