How to create an array in JavaScript whose indexing starts at 1?

Question

By default the indexing of every JavaScript array starts from 0. I want to create an array whose indexing starts from 1 instead.

I know, must be very trivial... Thanks for your help.

Solution 1

It isn't trivial. It's impossible. The best you could do is create an object using numeric properties starting at 1 but that's not the same thing.

Why exactly do you want it to start at 1? Either:

• Start at 0 and adjust your indices as necessary; or

• Start at 0 and just ignore index 0 (ie only use indices 1 and up).

Solution 2

A simple solution is to fill the zeroth item:

var map = [null, 'January', 'February', 'March'];
'First month : ' + map[1];

Semantically it would be better to use an object:

var map = {1:'January', 2:'February', 3:'March'};
'First month : ' + map[1];

Note these keys are not ints actually, object keys are always strings.
Also, we can't use dot notation for accessing. (MDN - Property Accessors)

I'd choose the first solution, which I think is less confusing.

Solution 3

Since this question also pops up for a Google search like "javascript start array at 1" I will give a different answer:

Arrays can be sliced. So you can get a sliced version of the Array like this:

var someArray = [0, 1, 2, 3];

someArray.slice(1);
[1, 2, 3]

someArray.slice(2, 4);
[2, 3]

Source: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/slice

Solution 4

You could use delete to remove the first element like so:

let arr = ['a','b','c'];
delete arr[0];

console.log(arr[0]);
console.log(arr[1]);

Or just not define it at all:

let arr = [,'b','c'];

console.log(arr[0]);
console.log(arr[1]);

If you want to make sure that you always get the first truthy element regardless of the index and have access to ES6 you can use:

arr.find(Boolean)

View more solutions

Comments

[detj]

Impossible...dats surprising! Well, there's no useful reason for me to say...why I want to start at 1...just an idea. So, yeah..i guess, I have to adjust my indices accordingly, which is not a problem. Wanted to start at 1, just for the sake of it.

[Michał Perłakowski]

This doesn't work with many array methods. For example, Array.from(myArray.keys()) returns [0, 1, 2, 3, 4] instead of [1, 2, 3, 4, 5].

[Ramin Bateni]

@Gothdo, i think you're wrong! ‌Because this result >> [0, 1, 2, 3, 4] has not any unexpected value for @detj (questioner). He just need ([0, 1, 2, 3, 4])[n] when n>=1.So this array always has correct result for him.

[xpuu]

Now, 8 years later, you can use Map

[josefdev]

How do I ignore index 0 in Javascript?

[Matt Korostoff]

This just creates an array whose first value is 1. This question was about how to create an array where the first index is 1, which is a very different thing.

[ToolmakerSteve]

@josefdev - put a value there, and then never refer to it. I.E. a = ["ignore me", "this has index 1", "another string, at index 2"]; firstString = a[1]; However, this advice isn't very useful - built in functions such as for (s of a) won't 'know' that you want to ignore a[0] - the burden is entirely on you to find ways to code that don't use a[0]; it is more practical to get used to arrays starting at 0.

[General Grievance]

Sorry, but I'm not entirely sure what this is suggesting. It looks like you already have the 1-indexed array before you use map.