Usage of new Array() and var arr=[] in javascript-JS Tutorial-php.cn

Everyone is learning the array functions new Array() and var arr=[] in JavaScript. Many friends don’t know the difference or usage. Let me analyze the array functions new Array() and var arr= in JavaScript. []The usage difference, let’s learn it together.

Let’s take a look at our summary.

var arr=[]

This is a literal method of defining an array

var arr=new Array()

This is the array generated by calling the array constructor

The above two methods of defining arrays are the same and different

Currently we generally agree on the following:

Using the new keyword to open a storage address in the memory consumes resources and memory.

The literal method is relatively simple to directly open a storage field in the memory and does not consume resources.

Let’s not deny the above conclusion first.

First of all, functionally speaking, var =arr=[] and var arr= new Array() are the same.

Then let’s use a piece of code to verify it

var startTime=new Date().getTime(); var test1=[]; var test2=[]; for(var i=0;i<1000000;i++){ //test1[i]={}; test2[i]=new Object(); } var endTime=new Date().getTime(); console.log('输出耗时:',endTime-startTime);

Copy after login

Each element in the above test1 and test2 arrays is an array , you can comment any line of code in sequence. I tested it more than 10 times.

The results

36**
36**

are the 2 above The time taken is about 3600 seconds, up and down, without any big difference

My running time is MacBook Air (13-inch, Mid 2013), processor: 1.3 GHz Intel Core i5, memory: 4 GB 1600 MHz DDR3, JS Runner tool

So let’s think that there is not much difference between the above two methods.

[] and new Array() are syntactically The only difference is that new Array() can directly set the length of the array.

new Array() has the following methods when constructing the array

var arr = new Array();
var arr = new Array(8);
var arr = new Array("c", "d", "e");
Literal method
var d = ["111", " 222", "333"];

So there is not much difference between the two methods in terms of performance. It is just a usage habit, and the literal value is more straightforward.

Exit To put it another way, if I use var arr=['111','222','333']; when defining an array, doesn't it open a storage address in the memory through the constructor?

Summary of some common methods of array Array in js

var list = new Array() is what we often write in js To the code, today I will summarize what methods the Array object has.

list[0] = 0;

list[1] = 1;

list[2] = 2;

Or declare it like this: var list = [0,1,2]

1 shift()t: Delete the first element of the array and return the deleted value. Here is 0

2 unshift(3,4): Load the parameters into the front of the array and return the length of the array. Now list: is 3,4,0,1,2

3pop(): delete the last element of the array and return the deleted value. Here is 2.

4push(3): Load the parameters to the end of the array and return the length of the array. Now in the List: 0,1,2,3

5concat(3, 4): Splice the two arrays together.

6splice(start,deleteCount,val1,val2,...): Delete the deleteCount item from the start position and insert val1, val2,...

reverse: Reverse the array
var a = [1,2,3,4,5];
var b = a.reverse(); //a: [5,4,3,2,1] b :[5,4,3,2,1]

sort(orderfunction): Sort the array according to the specified parameters
var a = [1,2,3,4,5];
var b = a.sort(); //a：[1,2,3,4,5] b：[1,2,3,4,5]

slice(start,end ): Returns a new array composed of items from the specified start index to the end index in the original array
var a = [1,2,3,4,5];
var b = a.slice (2,5); //a: [1,2,3,4,5] b: [3,4,5]

join(separator): Combine the elements of the array into a string , with separator as the separator, if omitted, the default comma is used as the separator
var a = [1,2,3,4,5];
var b = a.join("|"); //a: [1,2,3,4,5] b: "1|2|3|4|5"

The above content is the usage of new Array() and var arr=[] in javascript Difference_javascript skills, I hope it can help everyone.

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