You want the splice function on the native array object.
arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert).
In this example we will create an array and add an element to it into index 2:
var arr = [];
arr[0] = "Jani";
arr[1] = "Hege";
arr[2] = "Stale";
arr[3] = "Kai Jim";
arr[4] = "Borge";
console.log(arr.join()); // Jani,Hege,Stale,Kai Jim,Borge
arr.splice(2, 0, "Lene");
console.log(arr.join()); // Jani,Hege,Lene,Stale,Kai Jim,BorgeUPDATE (24 May 2024)
You can now use the toSpliced method which behaves just like splice, however it returns a new array without mutating the existing one.
You could update the previous example like so:
const updated = arr.toSpliced(2, 0, "Lene");
You want the splice function on the native array object.
arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert).
In this example we will create an array and add an element to it into index 2:
var arr = [];
arr[0] = "Jani";
arr[1] = "Hege";
arr[2] = "Stale";
arr[3] = "Kai Jim";
arr[4] = "Borge";
console.log(arr.join()); // Jani,Hege,Stale,Kai Jim,Borge
arr.splice(2, 0, "Lene");
console.log(arr.join()); // Jani,Hege,Lene,Stale,Kai Jim,BorgeUPDATE (24 May 2024)
You can now use the toSpliced method which behaves just like splice, however it returns a new array without mutating the existing one.
You could update the previous example like so:
const updated = arr.toSpliced(2, 0, "Lene");
You can implement the Array.insert method by doing this:
Array.prototype.insert = function ( index, ...items ) {
this.splice( index, 0, ...items );
};
Then you can use it like:
var arr = [ 'A', 'B', 'E' ];
arr.insert(2, 'C', 'D');
// => arr == [ 'A', 'B', 'C', 'D', 'E' ]
I have an array of, let's say, book pages sorted by chapter. I want to insert a new page every time a page's chapter is different from the previous.
The only way I know how to do that is to create a new empty array and then iterate through my books with Array.forEach() to push into that new array. I don't like it because you shouldn't need to rewrite a book just to add pages. What if instead of a book it was a shelf of books and I wanted to insert something between the books, should I buy a second shelf from Ikea just for that?
This basically:
(page, array) => { if(page.chapter.id !== array[index - 1].chapter.id) { return [page.chapter, page]}}
I tried Array.reduce but the accumulator is a nightmare to push. It just doesn't want to be iterable and I understand that reducers de-arrays the thing.
I tried array.map but I didn't manage to return two elements (the chapter page and the first page of that chapter). I think it messes with the index.