Detailed explanation of JS method of merging two arrays

1. Preface

During project development, it is very common to combine two arrays into one. for example:

var a = [1,2,3];
var b = [4,5,6];

There are two arrays a and b, and the requirement is to combine two arrays into one. The implementation method is as follows:

2. Realization

2.1 concat

ES5ofArrayThe object provides aconcat()method, concatenate two or more arrays and return the result.

var c = (b); //c=[1,2,3,4,5,6];

There is a question here,concatAfter the method connects the two arrays a and b, the data of the two arrays a and b remains unchanged, and a new array will be returned at the same time. In this way, when we need to combine multiple times, it will cause a lot of memory waste. If the amount of data is relatively small, it can be used barely. If the amount of data is large, this is inappropriate, so this method is definitely not the best.

2.2 for loop

The general idea is: iterate through one of the arrays and add all the elements in the array to another array in turn.

for( var i in b)
{
  (b[i]);
}

This way of writing can solve the waste of memory in the first solution, but there will be another problem: ugly! It makes no sense to say this. If you can do it with just one line of code, wouldn't it be great~

2.3 apply

FunctionalapplyThe method has a feature, that is(obj,argv)，argvis an array. So we can take advantage of this and go straight to the code:

(a,b);

Call this function instanceapplyMethod, and pass a and b as parameters at the same time, so that this method will traverse all elements of the b array to achieve the effect of merging.

It may be a bit confusing here, we can think of b as [4,5,6] and become like this:

(a,[4,5,6]);

Then the above operation is equivalent to:

(4,5,6);

This will be very clear!

In addition, two small issues should be paid attention to:

1) The above three merging methods have not considered which of the two arrays a and b is smaller in length. So a good way is to pre-judgment which of the two arrays a and b is larger, and then use large numbers to combine and small arrays, which reduces the number of array elements operations!

2) Sometimes we don’t want the original array (a, b) to change, so we can only use `concat`.

2.4 ...Extension Tag

ES6Provides extension symbol…Implement combination and merge.

var array_1 = ['reese','root','fusco'];
//["finch", "shaw", "bear", "reese", "root", "fusco"]
var array_2 =['finch','shaw','bear',...array_1];

This is the end of this article about the detailed explanation of JS merging two arrays. For more related JS merging array content, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!