Javascript Push/Shift same element multiple times

Question

I have the following code:

var foo = 'foo'
var bar = 'bar'
var arr = [1,2,3]

I want to add to foo several times at the beginning of the array and bar at the end of the array. The number of times each element added should be dynamic and the resulting array should be something like:

['foo','foo',1,2,3,'bar',bar','bar']

Is there a better method than using a loop for each element?I could use lodash if needed.

Simple answer, no.

Baruch
– Baruch

2017-08-19 10:31:29 +00:00
Commented Aug 19, 2017 at 10:31 — Baruch
– Baruch, Commented Aug 19, 2017 at 10:31

Jonas Wilms · Accepted Answer · 2017-08-19 10:58:36Z

16

If better means shorter, yes there's a way:

 var foo = 'foo';
 var bar = 'bar' 
 var arr = [1,2,3]

 var result = [
   ...Array(2).fill(foo),
   ...arr,
   ...Array(3).fill(bar)
];

edited Aug 19, 2017 at 10:58

user663031

answered Aug 19, 2017 at 10:32

Jonas Wilms

139k20 gold badges164 silver badges164 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Rahul Desai Over a year ago

I like this solution (+1) but FYI - doesnt support IE < 12 developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

keja · Accepted Answer · 2017-08-19 10:52:31Z

2

Or something like this.

var foo = Array.from({length:2}, v => 'foo');
var bar = Array.from({length:3}, v => 'bar');
var arr = [1,2,3]

arr.push(...bar);
arr.unshift(...foo);
console.log(arr);

answered Aug 19, 2017 at 10:52

keja

1,3631 gold badge15 silver badges21 bronze badges

Comments

prasanth · Accepted Answer · 2017-08-19 10:32:08Z

1

Try this forloop method. Array#unshift() added the value on starting of array.push add with end of the array

var foo = 'foo'
var bar = 'bar'
var arr = [1,2,3]

for(var i=0; i<(Math.random() * 5); i++){
arr.unshift(foo)
}
for(var i=0; i<(Math.random() * 5); i++){
arr.push(bar)
}
console.log(arr)

answered Aug 19, 2017 at 10:32

prasanth

22.6k4 gold badges33 silver badges57 bronze badges

Comments

marvel308 · Accepted Answer · 2017-08-19 10:39:09Z

0

You can use unshift and push like

function pushToBeginning(arr, str, count){
    while(count--){
        arr.unshift(str);
    }
}

function pushToEnd(arr, str, count){
    while(count--){
        arr.push(str);
    }
}

let arr = [1, 2, 3];

pushToBeginning(arr, 'Foo', 3);
pushToEnd(arr, 'Bar', 2);

console.log(arr);

answered Aug 19, 2017 at 10:39

marvel308

10.5k3 gold badges24 silver badges32 bronze badges

Comments

Gangula · Accepted Answer · 2023-05-24 05:41:18Z

0

most of the answers here use spread syntax or for loops to push. But its recommended to use Array.concat() for better performance & to avoid stack overflow error:

var foo = 'foo';
var bar = 'bar'
var arr = [1, 2, 3]

var result = arr.concat(Array(2).fill(foo), Array(3).fill(bar));
console.log(result)

Note that - according to this answer Array.fill is only recommended for primitive data types.

for non-primitives, you need to use Array.from because then all elements in the array will reference the same object in memory, so mutations to one item in the array will affect every item in the array

edited May 24, 2023 at 5:41

answered May 24, 2023 at 5:35

Gangula

7,8005 gold badges53 silver badges95 bronze badges

Collectives™ on Stack Overflow

Javascript Push/Shift same element multiple times

5 Answers 5

1 Comment

Comments

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

1 Comment

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related