How to merge two arrays in javascript

The methods of merging two arrays are:

Method one: use concat

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

var c = a.concat(b);

 //c=[1,2,3,4,5,6];

Method 2: Use loop

for(  let i in b){
 a.push(b[i])
 }

Method three: use apply

a.push.apply(a,b);

in When merging arrays, you can first judge the size of the arrays. It is obviously faster to merge the larger ones with the smaller ones.

If you do not want to change the arrays, it is recommended to use the concat method.

Recommended tutorial: js introductory tutorial

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