What is the difference between the usage of new Array() and var arr=[] in javascript?

Let me analyze the difference between the usage of array functions new Array() and var arr=[] in JavaScript. Let’s learn together.

Many friends don’t know how to distinguish or use the array functions new Array() and var arr=[] when learning JavaScript. Let’s take a look at our summary below.

var arr=[]

This is a literal method of defining an array

var arr=new Array()

This is a calling array The array generated by the constructor

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

Currently we generally agree on the following

Use the new keyword to remove memory Opening up a storage address 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 us not deny the above conclusion first. No.

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(&#39;输出耗时:&#39;,endTime-startTime);

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

Result

36**
36**

The two times above are both about 3600 seconds, up and down, there is no 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 there is not much difference between the above two methods.

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

new Array() has the following methods when constructing an 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 these two methods in terms of performance, it is just a usage habit, and the literal value is more straightforward.

Taking a step back, 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 the code we often write in js, Today I will summarize what methods Array objects have.

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 is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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