Mixed usage method of js one-dimensional array, multi-dimensional array and object

The main purpose of this article is to explain the mixing use of JavaScript arrays and objects. Due to the weak checking characteristics of JS, different types of variables can be stored in JS arrays at the same time. For example, you can put numbers, strings, characters, objects and other contents in the same array. Objects can do the same thing, the difference is that objects can specify the alias for each member of the object, so that the data is easier to read when programming, such as:

var arr1 = ["flying fish", 25, 172, "Jiangsu"];
var person = {name:"flying fish",age: 25, height:172,province: "Jiangsu"};

In this way, is it easier to read and use than arr1[0]? Of course, arrays and objects have their own advantages. The focus of this article is to combine the advantages of the two and use them in a comprehensive manner.

One-dimensional array
The following code creates an array called cars: first create the array, then assign values ​​one by one

var cars=new Array();
cars[0]="Audi";
cars[1]="BMW";
cars[2]="Volvo";

Or (condensed array): Assign values ​​when creating array objects

Two-dimensional and multi-dimensional arrays:
1. Create a two-dimensional array method one: first create a one-dimensional array, and then all members of the one-dimensional array create one-dimensional data

var persons = new Array();

persons[0] = new Array();
persons[1] = new Array();
persons[2] = new Array();

persons[0][0] = "zhangsan";
persons[0][1] = 25;
persons[1][0] = "lisi";
persons[1][1] = 22;
persons[2][0] = "wangwu";
persons[2][1] = 32;
persons[0] = ["zhangsan", 25];
persons[1] = ["lisi", 21];
persons[2] = ["wangwu", 32];

Compared with the previous method, this is much simpler and easier to read.

4. Summary
Although the first and second methods are a little more troublesome, the cost is that you can first create an empty multi-dimensional array and then assign values ​​in the for loop according to your needs. The third method is relatively simple and easy to use for enumerating data.
The last problem with two-dimensional arrays is what is the length of a two-dimensional array or a multi-dimensional array? Let's test the following code:

5. How to return the number of elements in a multi-dimensional array

The following array:

By multiplying the number of dimensions (here is 3) by the number of elements per dimension (here is 2) you can find that the number of elements in the multidimensional array is 6. But this is not an insurance policy, because the number of elements in each dimension in a multi-dimensional array can be different, such as:

The second element array of the first dimension of the array contains three elements, and the others have only two. This is still 3 if length is used to calculate, because the number of elements in the first dimension has not changed. However, it is wrong to use the above method to calculate the number of elements in the multi-dimensional array.
Therefore, the length attribute of a multi-dimensional array is the same as a one-dimensional array, and always returns the number of elements of the first-dimensional array. To calculate the number of elements in a multi-dimensional array, you can create one or more nested for loops yourself to calculate, such as:
When you know the dimensions of an array, you can write algorithms for this array, such as two-dimensional arrays:

var persons = [["zhangsan", 25], ["lisi", 21], ["wangwu", 32]];
function getArr2ElementNum(arr) {
var eleNum = 0;
if (arr == null) {
return 0;
}
for (var i = 0; i < ; i++) {
for (var j = 0; j < arr[i].length; j++) {
eleNum++;
}
}
return eleNum;
}
alert(getArr2ElementNum(persons));

When there are too many multi-dimensional array dimensions and complex nesting, it is too tiring to write the algorithms targeted through the above method, especially when this complex multi-dimensional array may also transform the dimensions at any time. The following complex multi-needed multi-dimensional array:
var arrN = [["zhangsan", 25, [1, "wangyuchu", 54, [123, 34, 16]], 43], ["lisi", 21, 172], ["wangwu", 32, "suzhou"]];
Even some multi-dimensional nested arrays are more complicated than this, so how do you calculate the number of array elements? I wrote a function to calculate the number of array elements. No matter whether it is one-dimensional or multi-dimensional, or no matter how complex nested multi-dimensional arrays it is, it can be calculated. The algorithm is not troublesome, and it mainly uses the concept of recursion:
//Distinguish whether an object is an array

function isArray(obj) {
return obj && ( typeof obj === 'object') && ( == Array);
}

//The initial value of the eleNum variable is 0, which is used to count the number of array elementsvar eleNum = 0;

//Recursively calculate whether an array element is a next-dimensional array. If yes, continue to recurse; if not, count the number of elements.function recursion(obj) {
if (isArray(obj)) {
for (var j = 0; j < ; j++) {
if (!isArray(obj[j])) {
eleNum++;
continue;
}
recursion(obj[j]);
}
} else {
eleNum++;
}
}

//arr is a one-dimensional or multi-dimensional array that wants to calculate the number of array elements, and returns the number of array elements by calling the recursion function recursionfunction getArrNElementNum(arr) {
if (arr == null) {
return 0;
}

recursion(arr);

return eleNum;
}

//Arbitrarily define a complex multi-dimensional nested arrayvar arrN = [["zhangsan", 25, [1, "wangyuchu", 54, [123, 34, 16]], 43], ["lisi", 21, 172], ["wangwu", 32, "suzhou"]];
//Print out the number of array elementsalert(getArrNElementNum(arrN));

Object:
Objects are separated by curly braces. Inside parentheses, the object's properties are defined in the form of name and value pairs (name : value). Attributes are separated by commas:

var person={
firstname : "Bill",
lastname : "Gates",
id    : 5566
};

There are two ways to address object properties:
Example

name=;
name=person["lastname"];

Mixed use of objects and multidimensional arrays:
Imagine such a scenario, and enumerate and count how many departments are there in the three universities, Tsinghua University, Peking University, and Zhejiang University, and how to do it?
First, create an array that includes three schools: