Say I've got an array:
[1,2,3]
And I want an array:
[1,2,3,1,2,3]
Is there a way to do that without looping through the array and pushing each element?
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5 Answers
You can use Array.prototype.concat()
let array1 = [1,2,3]
console.log(array1.concat(array1))
3 Comments
nwhaught
Perfect. Just didn't know what to call it in my searches. Thanks!
Antoine Gautrain
@adiga thanks I didn't know how to do it without jsfiddle or something like that :)
You can use spread syntax
let array = [1,2,3];
array.push(...array);
console.log(array)
answered Mar 22, 2019 at 15:28
Krzysztof Krzeszewski
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3 Comments
Krzysztof Krzeszewski
@MaheerAli i kinda make a use of both,
array.push function gathers any number of arguments with rest parameters, however i get a list of arguments from an array with spread operator
adiga
@MaheerAli this is spread syntax.
rest is when one collects multiple elements while destrucutring and in function arguments
Maheer Ali
@adiga thanks for info. I misunderstood a little bit
If you want to duplicate the array n times, you could use Array.from() and flatMap like this:
let duplicate = (arr, n) => Array.from({length: n}).flatMap(a => arr)
console.log(duplicate([1,2,3], 2))Comments
Here's with ES6 way of using concat:
let array1 = [1,2,3]
array1 = [...array1, ...array1]
console.log(array1)And here's for number of length you desire for:
let array1 = [1,2,3];
let ln = array1.length;
let times = ln * 2;
array1 = Array.from({length:times}, (e, i)=>array1[i%ln])
console.log(array1)This will allow you to stop at certain length if you wish. For eg.:
// result: [1,2,3,1,2]
let array1 = [1,2,3];
let ln = array1.length;
let times = ln * 2 - 1;
array1 = Array.from({length:times}, (e, i)=>array1[i%ln])
console.log(array1)
answered Mar 22, 2019 at 15:37
Bhojendra Rauniyar
86k36 gold badges179 silver badges241 bronze badges
Comments
Here's a variant with reduce
[1, 2, 3].reduce( (acc, item, index, arr) => { acc[index] = acc[index+arr.length] = item; return acc}, [] )
