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"..." operator in Javascript [duplicate]

I found the following case in javascript. I don't understand '...' operator mean here. I search it on the Google, but I did not get anything about it. Is there any other usage for this operator? Can someone help me out?

var x= [1,2,3];
var y = [4,5,6];

var z = [...x, ...y]; // z will be [1,2,3,4,5,6];

Thanks.

like image 353
xiaoke Avatar asked Oct 29 '25 12:10

xiaoke


1 Answers

I have a way of thinking which makes it very easy to understand and remember how '...' works.

var arr = [1,2,3] // this is arr which is the array

on the other hand

...arr            // this is whatever inside arr, which is 1,2,3

So you can also think of it as taking what is inside of an array.


Note that by its own, ...arr is not a valid syntax. You can use it in many ways , two of them coming to my mind are :

1 - Pass what is inside an array to a function

var arr = [ 1,2,3 ]
var myFunc = function(a,b,c) {
  console.log(a,b,c)
}
myFunc(..arr)   // logs 1 2 3

myFunc(1,2,3)   // logs 1 2 3

2 - Take what is inside of an array and use them in another array.

var arr = [ 1,2,3 ]
var foo = [ ...arr, 4,5,6 ] // now foo is [ 1,2,3,4,5,6 ]
like image 154
FurkanO Avatar answered Oct 31 '25 03:10

FurkanO