js declares an array, declares a map

1. Declare an array

1. Declare an empty array

var myArray = [];

var myArray1 = new Array();

var myArray2 = new Array(3);

It does not affect the assignment of the value exceeding the specified length.

2. Declare an array with values

var myArray3 = [1,2,3];

var myArray4 = new Array(1,2,3);

var myArray5 = new Array("3");

If the array has only one number, it needs to be quoted, otherwise it will think it has declared an array of length.

3. Assign values ​​to the array

myArray[0] = 12;

(13);

push means adding a new element to the end of the array

2. Declare map

1. Declare an empty map

var myMap = {};

2. Declare a valued map

var myMap1 = {
    key2:14,
    key3:15
};

3. Assign value to map

myMap1.key4=16;

myMap1['key5']=17;