@humanwhocodes/array-with-default

Array with Default Utility

by Nicholas C. Zakas

If you find this useful, please consider supporting my work with a donation.

Description

A class that represents an array where missing elements return a specified default value.

The built-in JavaScript Array class automatically returns undefined when you attempt to access a missing element. Here's an example:

const items = [1, , 3];
console.log(items[1]);      // undefined

In most cases that is okay, but in some cases you may want an alternate default value returned. The ArrayWithDefault class does that:

const items = new ArrayWithDefault({
    default: 0
    elements: [1, , 3]
});

console.log(items[1]);      // 0

The primary use case for this class is when an array is an optional argument for a function, but using an empty array won't work.

Usage

Node.js

Install using npm or yarn:

npm install @humanwhocodes/array-with-default --save

# or

yarn add @humanwhocodes/array-with-default

Import into your Node.js project:

// CommonJS
const { ArrayWithDefault } = require("@humanwhocodes/array-with-default");

// ESM
import { ArrayWithDefault } from "@humanwhocodes/array-with-default";

Deno

Import into your Deno project:

import { ArrayWithDefault } from "https://cdn.skypack.dev/@humanwhocodes/array-with-default?dts";

Browser

It's recommended to import the minified version to save bandwidth:

import { ArrayWithDefault } from "https://cdn.skypack.dev/@humanwhocodes/array-with-default?min";

However, you can also import the unminified version for debugging purposes:

import { ArrayWithDefault } from "https://cdn.skypack.dev/@humanwhocodes/array-with-default";

API

After importing, create a new instance of ArrayWithDefault. The constructor expects one object argument with the following properties:

• default (required) - the default value to return for the missing items.
• elements - an optional iterable object used to populate the array.
• length - an optional value to set the array's length property to.

Here are some examples:

const items = new ArrayWithDefault({
    default: 0,
    elements: [1, , 3]
});

// missing elements return the default
console.log(items[1]);      // 0

// elements after the end of the array return undefined
console.log(items[10])      // undefined

// elements whose value are undefined return the default
items.push(undefined);
console.log(items[3]);      // 0

const emptyItems = new ArrayWithDefault({
    default: 0,
    length: 5
});

// all elements return 0
console.log(emptyItems[0]);     // 0
console.log(emptyItems[1]);     // 0
console.log(emptyItems[2]);     // 0
console.log(emptyItems[3]);     // 0
console.log(emptyItems[4]);     // 0

// items past the end still return undefined
console.log(emptyItems[5]);     // undefined

Developer Setup

• Fork the repository
• Clone your fork
• Run npm install to setup dependencies
• Run npm test to run tests

License

Apache 2.0