Norse Polytheistic Mythology


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    Like an array, but rounder.


    Hoopy is a circular array data type. It extends Array so that out-of-bounds indices wrap back round to the start of the array (or if they're negative indices, they wrap back round to the end of the array).

    What's it useful for?

    If you want a fixed-length buffer for streamed I/O, Hoopy can do that for you.

    How do I install it?

    Via npm:

    npm i hoopy --save

    Or if you just want the git repo:

    git clone

    How do I use it?

    Loading the library

    const Hoopy = require('hoopy');

    Creating arrays

    const hoopy = new Hoopy(10);

    You must pass a size argument to the Hoopy constructor, otherwise it will throw.

    Accessing array items

    for (let i = 0; i < hoopy.length; ++i) {
      hoopy[i] = i;

    You can read and write array items using square brackets for indexing as you would with a normal array. However, if you write to an out-of-bounds index, it will not increase the length of the array. Instead the index is applied modulo the array length, wrapping back round to the start. Negative indices work in reverse, wrapping back round to the end of the array.

    The methods push, pop, shift and unshift will throw if called. Future versions of the library may implement sane behaviour for them. All of the other Array methods work normally.

    Growing the array


    The grow method adds items to the array. It takes one argument, which is the number of items to grow the array by. The new length of the array will be the old length plus the number you pass to grow.

    If the current state of the array includes overflowed indices, grow will take care to move those items in to the freshly-created available space, so that the correct order is maintained for your data.

    The caller is responsible for ensuring they don't overwrite unprocessed items. If you need to increase the size of the array, you must call grow.

    Is there a change log?


    How do I set up the dev environment?

    To install the dependencies:

    npm i

    To run the tests:

    npm t

    To lint the code:

    npm run lint

    What license is it released under?



    npm i hoopy

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    • philbooth