simple, explainable reactivity

auto is a reactivity tool for javascript.

how it looks

just one keyword auto is used like this:

let $ = auto({
    data: null,
    count: ($) => $.data ? $.data.length : 0,
    msg: ($) => $.data + " has " + $.count + " items"

see docs/ for a breakdown of the syntax.


whenever you use the returned object

$.data = [1,2,3];
console.log("msg =",$.msg);

everything will update automatically so for example the above will print

msg = 1,2,3 has 3 items


it's worth reading docs/ and docs/ first

what distinguishes auto from other reactive libraries?


the auto library is 100 lines long, has no external dependencies and uses just five variables to manage its internal state; you can understand the whole thing. see docs/ for a walk-through of the code and also docs/devlog for a blow-by-blow account of its development and design choices.




auto's internal variables are easy to interpret: looking at them explains behaviour. three can be viewed via the special _ member (the other two aren't useful for debugging) so


will print something like

    dep: ['count': ['data'], 'msg': ['data','count']],
    dirty: { msg: true },
    value: { data: [1,2,3], count: 3 }

see docs/ for a walk-through on what these variables mean.


you can use auto with node/npm, as an es6 module and directly in the browser.

npm and node

to use via npm install with npm install @autolib/auto and then you can import it with const auto = require('@autolib/auto';. see docs/ for a detailed walkthrough.

es6 module

for this simply use the right lib in the import, i.e.

const auto = import('auto-es6.js');

and to test you could use, for example, deno i.e. deno run test.js. you could use docs/ as a template (just replace the import statement).


to use directly in a <script> tag use auto-no-import.js. see docs/ for a walk-through.


auto was originally developed to be used with Svelte (see below) but other specific integrations with React, Vue, Mithril etc. still need to be done. however auto's subscribe method makes it easy to tie it into any existing framework.






this library started as an attempt to create MobX-like observables in Svelte. that original version was based largely on a video by MobX's creator (see the docs/ for more on this). then a new approach written up from scratch in a day which was documented with extreme detail in docs/devlog.

what's left out

what i can imagine some people might want in auto (because of what i've seen in other reactive libraries) but that i left out on purpose.


there was a version of the old library (mobx-svelte) that had nested reactivity (because i saw the MobX creator use it in the video that started this) but i didn't put it into the new one. i'm still haven't come across a convincing use-case. i'm using auto in a very large project and never needed nesting. i'd rather leave it out for now.

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