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A very good W3school tutorial can be found here.

Insert an element at index and shift the tail of an array in Javascript

I had to achieve a quite specific task and as far as I checked I didn’t find existing solutions in there so I’m gonna share my work if it helps (I really hope I’m not issuing a duplicate, I found this question Shift array to right by adding a new element to left using js which is not really my goal)

I had to insert an element in an array at a given position, and shift the rest to keep the same order and length. For example:

let array = ['a', 'b', 'd', 'e', 'f'];
const idx = 2;
const new = 'c';

Then the expected output is ['a', 'b', 'c', 'd', 'e']

The question is now: how to proceed, without creating copies and explicitly looping the whole input array ?

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3

Answers


  1. Chosen as BEST ANSWER
    0

    So, I came up with this solution ─ don't hesitate to tell if there's a better way to do this !

    let array = ['a', 'b', 'd', 'e', 'f'];
const idx = 2;
const new = 'c';

array.splice(idx, months.length-idx, new).forEach((e, i, a) => {
  if (i < a.length-1) {
    months.push(e);
  }
});

    → splice returns an array with the removed elements: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice

    → forEach takes (element, index, array upon which forEach is called) as parameters: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach


  2. 0

    You could splice the array and adjust the length.

    const
    array = ['a', 'b', 'd', 'e', 'f'],
    index = 2,
    value = 'c';

array.splice(index, 0, value);
array.length--;

console.log(array);
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  3. 0

    As an alternative to Array::splice() you can use Array::copyWithin():

    const
    array = ['a', 'b', 'd', 'e', 'f'],
    index = 2,
    value = 'c';

array.copyWithin(index + 1, index);
array[index] = value;

console.log(array);
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